Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: Ring on September 22, 2004, 06:45:47 PM
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http://www.axishq.wwiionline.com/~ring/info/ammo/GlacierGirl20mm.wmv
Enjoy
that was a REAL
Hispano M2
20mm HEI 6.98 Tetryl +4.3g Incendiary
that was still in the gun when found...
what do you think a 20mm Minengeschoss with 18g PETN would do?
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Keep in mind that the US M2 20mm cannon is a Hispano Mk II cannon.
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and?
its the same 1 the brits used
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Mk 1 cannon, Mk 2 cannon...either way you slice it, that was still one damned big hole!:eek:
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No, from what I've read around the boards, The Mk2 was a bit better than the Mk1.
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I don't know what the M1 20mm cannon was, but I'm not sure it was related to the M2 20mm cannon.
The M2 is the same as the Hispano Mk II. I don't think we ever had an equivilent of the Hispnao Mk I. The Hispano Mk I had a 60 round drum magazine, the Hispano Mk II was belt fed.
Nice video now that I've seen it on a system that wasn't 50% artifacts.
That should give some people an idea of how the RAF/USAAF cannons were. Too often they Hispano/M2 gets painted as firing some AP round that would just punch a little hole and not do any real damage like the German rounds.
The bottom line was that getting hit by a 20mm round, any 20mm round, was really unhealthy.
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From the way it was laid out to me, the Mk2 20mm bullet is different than the Mk1 20mm bullet. Hence you had to have a different gun to shoot it.
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Was that drum filled with anything?
You guys haven't seen that MGFF-M round hit that wing section...
Nothing but confetti left.
Getting hit with a 20mm was bad.
Crumpp
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Originally posted by lasersailor184
From the way it was laid out to me, the Mk2 20mm bullet is different than the Mk1 20mm bullet. Hence you had to have a different gun to shoot it.
No, you must be thinking of the M1 and AN-M2 cannons, not the Mk I and Mk II 20mm cannons.
M1 and M2 are both US service names and do not indicate any relationship bewteen the cannons. In fact the M1 was a 37mm cannon.
Mk I and MK II are UK terms using, in this case, in relation to the Hispano-Suiza HS404 cannon. The Mk I being the original French cannon and the Mk II being the modified cannon for British service. The Hispano Mk I, Mk II and Mk V all chambered the same exact rounds.
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Originally posted by Crumpp
guys haven't seen that MGFF-M round hit that wing section...
Yes I have and it wasn't any more impressive. The little thing they'd built was just some aluminium wraped around a couple of wooden blocks. Not nearly as tough as a 55 gallon oil drum.
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Thier were some diferances between the US and British Built Hispanos, the US ones suffered from reliabality issues, largely do to how they were made, specificaly US tolerances differed (a bit slopy) and resulted in weapons that tended to jam, in fact they were so problematic that drastic meashures had to be taken to inshure their operation. In some instances I beleave P38's they were often removed, in F4U-IC's and the Helldive they had to superlube the ammo to make them work, and I beleave they still had issues after that had been done.
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Originally posted by brady
Thier were some diferances between the US and British Built Hispanos, the US ones suffered from reliabality issues, largely do to how they were made, specificaly US tolerances differed (a bit slopy) and resulted in weapons that tended to jam, in fact they were so problematic that drastic meashures had to be taken to inshure their operation. In some instances I beleave P38's they were often removed, in F4U-IC's and the Helldive they had to superlube the ammo to make them work, and I beleave they still had issues after that had been done.
That is true, but only because they (A) disregarded the British solution to shorten (or was it lengthen?) the breach by a couple of milimeters and (B) had the idiocy to manufacture it to artillery tolerences becaus e it was a "cannon" and therefore "aretillery".
Otherwise it was the same gun.
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None of the P-38 pilots I know had any real complaints with the 20 MM, other than it would have been nice to have more ammo. None of them ever said they had the 20 MM taken out either. There are however reports of P-38's having the 20 MM removed and multiple M2 50 BMG's added.
On a sadder note, Mr Roy is not nearly so well as he looked in that video. He was not very well at all last year when I spoke with him. He is a wonderful man who dearly loves that plane with all his heart. He absolutely lives to have people see his baby.
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I am sorry to hear about Mr Roy. I hope that he feels better soon.
:(
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Originally posted by Karnak
Yes I have and it wasn't any more impressive. The little thing they'd built was just some aluminium wraped around a couple of wooden blocks. Not nearly as tough as a 55 gallon oil drum.
that was a test i made my self with my guns and HE =)
http://www.axishq.wwiionline.com/~ring/info/ammo/wing-test.wmv
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CC Karnak, I was going on purely memory and spaced the detail about the Artilery Tolerances.
..............
From what I understand on the P-38's this replacing of the 20mm was in part do to issues with the 20mm, also the reports I recal came largely from Pacific theater referances, at least the ones I recall do.
............
Ring, I thought that test was prety darn cool, espichaly the last shot with the 20mm.
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Yes I have and it wasn't any more impressive.
This is a lot more impressive:
http://www.axishq.wwiionline.com/~ring/info/ammo/wing-test.wmv
Than this:
http://www.axishq.wwiionline.com/~ring/info/ammo/GlacierGirl20mm.wmv
Getting hit with 20mm was bad but you cannot argue with more explosive. As they say in demolitions, the formula "P" for plenty works.
(http://www.onpoi.net/ah/pics/users/503_1095940082_mineammo.jpg)
Crumpp
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Crump,
How can you say that the first film is more impressive? The chunk blown out of the barrel was bigger than the entire structure in the first video and made of a much, much stronger materiel and structure.
The test of the German round was against something that was not large enough nor did it match any aircraft structure. The test while neat looking was done too poorly to tell us anything other than the round was explosive. The Hispano round would have blown that piece of aluminium and wood completely apart too. Yay. It doesn't tell us anything.
I have no doubt that the German round would put a bigger hole in an aircraft. However these tests don't tell us that. The explosive content does.
To do a real test would require an aircraft structure large enough to survive the blow. Then the respective damage could be compared. Say, a junked 707's wing or some such.
What I am getting at, and you are steadfastly ignoring, is the tendency of certain people to romatisize the German hardware to the point where they have drasticly unrealistic expectations of Allied hardware. There is a group of WWII buffs out there that would have claimed the Hispano round would simply have made a little hole in one side of the barrel, exploded inside, and made a small collection of tiny holes from shrapnel. That is clearly not what happened.
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Originally posted by Karnak
I have no doubt that the German round would put a bigger hole in an aircraft.
A would not classify as "hole" what a mine shell can do in an aircraft.
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Originally posted by GODO
A would not classify as "hole" what a mine shell can do in an aircraft.
Everything is a "hole", unless you claim that a hit from a mine shell would take a B-17's wing clean off.
If that is the case, you're delusional.
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Originally posted by Karnak
Everything is a "hole", unless you claim that a hit from a mine shell would take a B-17's wing clean off.
If that is the case, you're delusional.
Was thinking on a spit wing.
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MANDOBLE,
Talking about damage and relatively fragile aircraft is pointless.
Spitfire and Bf109 wings were prone to breaking off when strick by a 20mm round. That doesn't really tell us anything. You need to look at bigger things like Ju88, B-17 and Lancaster wings.
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Originally posted by brady
Thier were some diferances between the US and British Built Hispanos, the US ones suffered from reliabality issues, largely do to how they were made, specificaly US tolerances differed (a bit slopy) and resulted in weapons that tended to jam, in fact they were so problematic that drastic meashures had to be taken to inshure their operation. In some instances I beleave P38's they were often removed, in F4U-IC's and the Helldive they had to superlube the ammo to make them work, and I beleave they still had issues after that had been done.
Can't complain too much about reliabilty since that was a 50+ year old gun, firing 50+year old ammo after being locked in ice all that time :)
Dan/Slack
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Everything is a "hole", unless you claim that a hit from a mine shell would take a B-17's wing clean off.
You need to look at bigger things like Ju88, B-17 and Lancaster wings.
The Luftwaffe commissioned a study on A/C weapon effectiveness against the Heavy bombers.
It concluded that it took an average of 15 rounds off 20mm to guarantee the destruction of a Heavy Bomber.
The average fighter pilot could only land around 2 percent of his rounds on target. This meant an FW-190 firing it's total ammo load could only land between 10-12 rounds. Hence two fighters would be assigned to one bomber in order to ensure destruction.
Now it only took 2-3 rounds of Mk 108 30mm to have the same effect.
What I am getting at, and you are steadfastly ignoring, is the tendency of certain people to romanticize the German hardware to the point where they have drastically unrealistic expectations of Allied hardware.
Actually I think it is the other way around. People tend to view the Kinetic energy delivery of the Hispano's as much more powerful than the chemical energy of the M-Geschoss rounds.
You even hear the argument of M-Geschoss "bouncing off".
Anybody ever fly FA 2.5? The Hispano's were one-shot wonders and could hit out to 1800 meters while the MG151's were not much better than a. 50cal.
All based off of kinetic energy delivery calculations.
Facts are the Luftwaffe did a very good analysis of air-to-air weaponry and chose the correct philosophy. This is back by Tony William's excellent research into fighter armament effectiveness.
Now a fighter can take less damage. One or two rounds of any 20mm HE should give you a great chance of knocking it down.
Talking about damage and relatively fragile aircraft is pointless.
Absolutely correct.
Was thinking on a spit wing.
Would be destroyed, as would a 109 or a 190 wing that took a hit in the main wing spar from an allied 20mm. The allied shell would give a slightly higher chance of flying away but not by much.
Crumpp
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Originally posted by Karnak
MANDOBLE,
Talking about damage and relatively fragile aircraft is pointless.
Not exactly, these 20mm weapons and ammo were designed well before large bombers got into scene. The massive air war in the East front was mostly against light bombers and fighters. Most if not all the LW aircrafts and weapons since 42 to 44 were designed to fit into this front.
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You miss my point. It has nothing to do with the potential damage if a Hispano hit and a MG151/20 hit do the same thing. You need a target that survives to compare damage.
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Karnak, Im pretty sure most fighters will survive several hispano or MGFF-151/20 HE hits, except german 20mm mines, that is the point. Difference between any 20mm HE and mines are really relevant. Any fighter will keep in flying condition also with several or even lots of 20mm AP hits, except if pilot or engine is damaged.
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Difference between any 20mm HE and mines are really relevant.
Very good point. The M-Geschoss packs over twice the amount of chemical energy. I don't remember off hand exactly what it was but I think it is PETN but do remember that it has a very high E factor. Higher than TnT or C4. Combine the speed of the explosive with the raw amount and M-Geschoss would have ruined any pilots day.
Crumpp
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Originally posted by GODO
Karnak, Im pretty sure most fighters will survive several hispano or MGFF-151/20 HE hits, except german 20mm mines, that is the point. Difference between any 20mm HE and mines are really relevant. Any fighter will keep in flying condition also with several or even lots of 20mm AP hits, except if pilot or engine is damaged.
Which is exactly what I'm getting at. You guys act like the Hispano was AP. It was not. It is not punching little 20mm holes in the aircraft.
I don't have access to the quote, but I recall one BoB ear pilot who stopped combat flying just after the cannons were introduced. He later, I don't recall why, was flying a combat mission and fired a very short spurt at a Bf109, something like 6 rounds from each cannon, and the Bf109's wing was instantly blown off. He said he was very surprised because he had forgotten how powerful the cannon were.
As it didn't sound like he was particularly close or took careful aim it is unlikely many, or even multiple, rounds hit.
This constant talking down of the Hispano's lethality is really weird.
I agree that the mine round will do a lot more damage against the skin of an aircraft and weaker formings. Things like the fuselage of a Spitfire would be particularly vulnerable.
I don't know that the mine round is the garunteed one hit, one kill wonder round you make it out to be though. It is one thing against a Spitfirem but another against a P-47 and yet another against a Wellington or B-17.
FWIW, I pretty much consider a Hispano or MG151/20 HE hit a pretty likely kill against a Spitfire as well. That is why I don't think talking about hits to Spitfires is very productive.
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Which is exactly what I'm getting at. You guys act like the Hispano was AP. It was not. It is not punching little 20mm holes in the aircraft.
I know that and was not implying it did.
This constant talking down of the Hispano's lethality is really weird.
Not aware that anyone was taking down allied 20mm lethality.
I agree that the mine round will do a lot more damage against the skin of an aircraft and weaker formings. Things like the fuselage of a Spitfire would be particularly vulnerable.
It would have done lots of damage no matter where it hit.
I don't know that the mine round is the garunteed one hit, one kill wonder round you make it out to be though.
If it hit and went off, most likely it would be a kill with one round.
It is one thing against a Spitfirem but another against a P-47 and yet another against a Wellington or B-17.
Depending on the plane and it's structural strength, of course.
You have to remember that Cannon rounds were mixed just like MG belts. Not every round in the hopper was a M-Geschoss, HE, or AP. Usually they were mixed.
FWIW, I pretty much consider a Hispano or MG151/20 HE hit a pretty likely kill against a Spitfire as well. That is why I don't think talking about hits to Spitfires is very productive.
I think this springs from the fact that the MGFF in AH is a very very weak cannon when it should not be at all. The MG151's seem kind of weak as well. I lit a Spitfire up the other night in a Snapshot Scenario. Used nothing but MG151, he simply smoked and flew off like nothing happenend. Whether this is modeling, a bug, or a connection issue (got cable) I don't know.
I am certainly not attempting to attack the Hispano. It was a lethal air to air weapon. You've got some great info Karnack. Thanks for sharing.
Crumpp
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Karnak none I have read ever siad there were no Hispano HE rounds.
In 1942 the SAPI was introduced, and that plus the HEI became the standard loading for RAF fighters thereafter. Everyone knows this.
From Tony Williams site its just 8% HE material by weight where by the MGFF/M contains 22%.
He goes on to mention:
If we compare the values with the few data known from ballistic tests, we have some indications that the factors assumed in the calculations are realistic. The 20x80RB M-Geschoss and the 20x110 (Hispano) HE were rated as about equal; the greater blast effect of the M-Geschoss was countered by the greater penetration and kinetic damage inflicted by the Hispano. They do indeed emerge with similar scores.
What folks talk about is the disparity in lethality between the hispano and other 20 mm HE rounds in AH.
Folks have pointed out that the RAF didnt load AP Hispano rounds. Its SAPI round could penetrate 25mm (IIRC) of armor yet it flies around the main blowing mbts with ease.
The Hispano in AH is a hybrid HE/AP. Its high velocity at impact gives in far greater lethality it AH then the MGFF/M or the ShVak or the mg151/20.
I am sure the 109s use a hybrid round as well. Does it account for accurate belting and is the M-Geschoss if accounted for? The Hispano is a far more lethal round in AH then any other 20mm round.
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Wotan,
I'm not talking about AH. I am well aware of the issues in AH.
I was talking about reality,
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I'm not talking about AH. I am well aware of the issues in AH.
:)
There lies the confusion. WE are talking about AH! :p
Think I have some belting information for the LW. Let me dig around and see. Karnack, You have any info on the RAF?
Crumpp
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IIRC the MG151/20 was belted with 1xAP, 1xHE-T, and 2xHE-M. So every other round would be a HE-M, while every fourth round would be AP and HE-T respectively.
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Originally posted by GScholz
IIRC the MG151/20 was belted with 1xAP, 1xHE-T, and 2xHE-M. So every other round would be a HE-M, while every fourth round would be AP and HE-T respectively.
Dont think any mine is included in AH, nor every other round neither every 1000. If they are, HTC forgot to put any explosive in them.
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Found it and Gscholtz beat me to it.
I am not the most internet savy guy on the block...WTH does IIRC mean? Seen it used many times before.
Crumpp
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if I recall correctly
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Originally posted by Karnak
Wotan,
I'm not talking about AH. I am well aware of the issues in AH.
I was talking about reality,
What? Then why do you keep saying:
This constant talking down of the Hispano's lethality is really weird.
and
Too often they Hispano/M2 gets painted as firing some AP round that would just punch a little hole and not do any real damage like the German rounds.
Folks on this forum (I assume this who you are referring to by using "they") say the opposite. That RAF hisso's weren't loaded with AP and that the amount of HE was less then what was carried in other rounds like the MGFF/M. All the statements and threads that I have read on this subject and in this forum relate to game performance, not in "real life".
As I said we all know Hisso HE rounds were used. The dispute comes from the disparity between the Hispano and all other 20mm HE / Mine rounds in AH.
They aren't referred to as Hizookas for nothing.
The benefits of the Hispano are its mv which increases hit probrability at convergence and its flatter trajectory.
In AH its benefits are range and greater lethality. This is what folks talk about on this forum when the speak of the hisapno.
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Originally posted by Karnak
I was talking about reality,
Me too.
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if I recall correctly
Thanks Wotan.
GODO did you get those charts on the FW-190A3 I sent you?
Crumpp
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Originally posted by Crumpp
Thanks Wotan.
GODO did you get those charts on the FW-190A3 I sent you?
Crumpp
I'll check for these in 30 mins. Thanks Crumpp.
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The benefits of the Hispano are its mv which increases hit probrability at convergence and its flatter trajectory.
Anybody got a convergence chart for the Hispano. I have a ballistics chart for the FW-190A6 bis A9. The MG151's are fairly flat shooting 20mm. Muzzle velocity does not necessarily mean better trajectory or range. Lots of other factors can effect it.
Crumpp
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Tony Williams has stated on the forum that because of the size of the hispsano the Spit had to go with 300yrds. This was an issue for the RAF as they wanted 200.
Serach for his reply you will find it.
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Just fyi
Here's a limk to an RAF Gunnery Training manual
http://www.darts-page.us/files/gunnery01.htm
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Thanks Wotan!
Couldn't really tell what the convergence was set too from that. Based on some of the guns solutions from that last page I would be very surprised if the Hispano had a flat trajectory.
Crumpp
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You are right its not "flat" but "flatter" then say the mgff or the MG151/20.
Even the 50 and .303s arent "flat".
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The ballistics of the projectile can stand much improvement. It is believed that ballistics similar to that of the Caliber .60 projectile can be closely approximated.
http://www.quarry.nildram.co.uk/US404.htm
Ours, without a doubt. The ShVAK was twice as reliable. The Hispano simply required an unbelievable amount of maintenance. The smallest exposure to dust, congealed lubricant, or any other kind of little thing, and the gun would not fire. Very unreliable.
The ballistics of our cannon were better. Our cannon had a flatter trajectory, which is significant for applying lead. When you talk about the Yaks, then one didn’t even need a sight. The tracers were almost straight, take aim and fire, and where the nose is pointing is where the rounds struck.
http://airforce.users.ru/lend-lease/english/articles/golodnikov/part3.htm
If you scroll down you will see the ShVAK and MG 151 were very similar weapons.
http://www.geocities.com/CapeCanaveral/Hangar/8217/fgun/fgun-pe.html
So the higher muzzle velocity does not necessarily mean better ballistics.
http://www.quarry.nildram.co.uk/highvel.htm
Crown of the barrel, mounting, rifling, Barrel harmony, cartridge, all come into play and influence ballistics as you probably already know.
It's very similar to wing loading when examining plane turning performance. It is useful for "guestimation" but is not the whole picture which can change when other factors are considered.
Sum it all up. The difference between the MG151 and the Hispano I am willing to bet will be measured in a few cm's.
Crumpp
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A few comments: as has already been quoted in extracts from my site, the information I have indicates that there wasn't much difference in the overall lethality of the Hispano and the MG 151/20. One would be more effective in some circumstances, less in others.
The trajectory of a projectile is a function of two variables; the muzzle velocity and the ballistic coefficient of the projectile (which measures the air resistance, and thereby determines the rate at which the projectile slows down). The ballistic coefficient of a 20mm shell is also determined by by two variables; the weight (the heavier, the better) and the shape (the more streamlined, the better).
The Hisso had a higher muzzle velocity than either the MG 151/20 or the ShVAK. It also fired heavier projectiles than either. There wasn't much difference in the shape. So the Hisso shells would have a shorter flight time, and a flatter trajectory, than the other two, which helped in improving the hit probability.
Tony Williams: Military gun and ammunition website (http://www.quarry.nildram.co.uk) and Discussion forum (http://forums.delphiforums.com/autogun/messages/)
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The Hisso had a higher muzzle velocity than either the MG 151/20 or the ShVAK. It also fired heavier projectiles than either. There wasn't much difference in the shape. So the Hisso shells would have a shorter flight time, and a flatter trajectory, than the other two, which helped in improving the hit probability.
I agree. But what exactly is that difference?
Crumpp
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Originally posted by Crumpp
I agree. But what exactly is that difference?
I don't have specific BC information about the projectiles, but you can get a pretty good impression just by looking at the shape of the nose (there are cartridge illustrations linked to the 'WW2 Aircraft Gun Effectiveness article here: http://www.quarry.nildram.co.uk/WW2guneffect.htm ). The more tapered the nose, the better. This is of course complicated by the fact that different types of projectile for the same gun had different shapes, with AP generally been more pointed than HE.
Tony Williams
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FWIW that video is more aimed at CRS, WW2OL and their nerfed 20mm model (right Ring?).
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The more tapered the nose, the better. This is of course complicated by the fact that different types of projectile for the same gun had different shapes, with AP generally been more pointed than HE.
Thanks Tony for taking the time to post!
That one needs to get explained, Please. You may be familiar with SOTIC. In that course they teach it is the BACK of the bullet that determines the ballistics. I have cut the nose completely off bullets on a KD range and shot a 1/2 MOA group at 400 meters on a clean target. The cut bullet landed right in the group within normal bullet dispersion.
Nick the back of the bullet now and the ballistics completely change.
Different weights, manufacturing tolerances. humidity, tempature, blah blah blah (You know the factors...)
Will all effect your despersion. I have never heard that the nose had any real effects until impact.
Obviously the different weights of the different tapers will move your pattern.
It would be great to get a BC on the Hispano.
Crumpp
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The base of the bullet becomes more important at subsonic speeds, but at supersonic it's the profile of the nose which counts for most. Why do you suppose that long-range rifle bullets, rocket nose-cones and fighter noses taper towards a point at the front?
On my web article on 'Basic Ballistics', I have a 'rule of thumb' (derived from P O Ackley data - a famous ballistician) for calculating the BC of a bullet from the nose shape. You multiply the sectional density (which basically measures the length of the projectile) by a 'form factor' as follows:
Flat-nose lead: 0.8
Round-nose lead: 0.9
Round-nose jacketed: 1.0
Semi-pointed soft point: 0.9-1.1
Pointed soft point: 1.2-1.6 (depending on sharpness of point)
Pointed full jacket: 1.5-1.8
Pointed full-jacket boat-tailed: 1.9-2.0
To put it another way, the most streamlined kind of rifle bullet will lose velocity at only half the rate of a jacketed round-nosed bullet of the same calibre and weight.
Tony Williams: Military gun and ammunition website (http://www.quarry.nildram.co.uk) and Discussion forum (http://forums.delphiforums.com/autogun/messages/)
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Interesting.
I shoot high powered rifles at work quite a bit. In fact it was a .308 round we did this too:
I have cut the nose completely off bullets on a KD range and shot a 1/2 MOA group at 400 meters on a clean target.
In order to demonstrate that damaging the nose has no effect on the flight characteristics. Now changing the weight will have a dramatic effect. I was taught to file the nose to eliminate weight differences when reloading using a hand press in the field.
On my web article on 'Basic Ballistics', I have a 'rule of thumb' (derived from P O Ackley data - a famous ballistician) for calculating the BC of a bullet from the nose shape. You multiply the sectional density (which basically measures the length of the projectile) by a 'form factor' as follows:
I did not know this. Thanks for sharing.
I still would like too see the BC on the Hispano. I think it will be flatter but not nearly as dramatic as most people think. I will bet the differences will only be measured in a few centimeters.
Crumpp
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Crump,
A few centimeters at what range?
And can we say that you mean about 3 centimeters when you say the nonspecific "few"?
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Crumpp, more flatter, less flatter, well, not really important unless you are firing from a rigid platform that absorbs most of the gun vibrations, that may apply only to the P38 and Mosquito, the rest of hispano users have the guns at the wings and I doubt these "so powerful" wonders are also recoiless. I expect much more noticeable dispersion of these guns compared to the typical 151/20 mounting at the hub or wing roots. Outer 151/20 are a different story.
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A few centimeters at what range?
Max ord
I expect much more noticeable dispersion of these guns compared to the typical 151/20 mounting at the hub or wing roots. Outer 151/20 are a different story.
We will never know GODO. All we have is speculation since we have no BC for the Hispano.
In that the modelers definition of "flatter" becomes important.
Looking at the MG 151's ballistics I don't think the difference will be very dramatic. The Hispano will be flatter but not far off the MG 151.
Crumpp
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Originally posted by Crumpp
We will never know GODO. All we have is speculation since we have no BC for the Hispano.
BC? Ballistic coeficient? If so, it is related to the rounds only, totally independent of the gun or gun mounting. Lets say due ballistics alone we have a dispersion depending on muzzle velocity and BC, but there is other dispersion inducted by the gun itself and also affected by the gun mountings, the more rigid the mountings, the better, unless you have a gun that is able to absorb all the energy of every shot. The former dispersion is more evident as the round loses energy while the latter is applied since the very beginning of the shot. Hub, nose or wing root mountings are far more rigid than wing ones, and so, the gun inducted dispersion should be less noticeable.
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I recall one British document that noted that the Hispano mounting on the Mosquito was much more rigid than the Hispano mounting on the Typhoon.
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Originally posted by Karnak
I recall one British document that noted that the Hispano mounting on the Mosquito was much more rigid than the Hispano mounting on the Typhoon.
That is pretty obvious.
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To summ it up, aiming and hitting with Yaks, Las, 109s, 190s, P38s, 205s, Ki61s, 110s and mosquitos should be easier than with spits, TYphs, P47s, P51s, N1K2s, etc. Doesnt matter the flatter or less flatter trajectory, weapon mountings are a decissive factor.
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I wouldn't include the C.205 in that list and I'd say the jury is out in regards to the wing mounted cannons on the Fw190s.
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BC? Ballistic coeficient?
Ballistic Chart.
I'd say the jury is out in regards to the wing mounted cannons on the Fw190s.
No the Jury has recessed and gone home. The FW-190's ballistics are known factor. The BC for both the FW-190A5 and FW-190A8 are in the hands of Pyro.
;)
Crumpp
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Originally posted by Crumpp
No the Jury has recessed and gone home. The FW-190's ballistics are known factor. The BC for both the FW-190A5 and FW-190A8 are in the hands of Pyro.
I was not speaking of the BC. I was speaking of the rigidity of the cannon's mounting point and it's effect on dispersion.
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I was not speaking of the BC. I was speaking of the rigidity of the cannon's mounting point and it's effect on dispersion.
I would think the wingroot would be a very stable mount. It seems to be a favoured position if they can get the gear out of the way.
Crumpp
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"Jury" term is out of my very limited english vocabulary, but, of course, 190A outer guns would induct more dispersion than wing root ones.
Hohun posted interesting dispersion numbers in the thread about MG-FF dispersion confirming that MG-FF were, in fact, sniper weapons. Trajectory is secondary when you have an accurately marked gunsight and accurate guns, dispersion is the big gunsight nullifier factor.
Wing roots are probably the more rigid part of a plane, nose weapons are still dependent of direct engine vibrations.
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MANDOBLE,
You're english is very good. What I meant about the wing root guns is that it is not known how rigid their mountings were. I'd think they'd be better than guns like the C.205 and Spitfire have, but worse than engine mounted guns or fuselage guns like the Bf110, Mossie or P-38.
As to the MG/FF / Type 99 Model 1, well, muzzle velocity means a whole lot more than you're giving credit. The were not "sniper weapons", no automatic cannon was. Further, muzzle velocity plays a very large part in hitting a small, moving target. Under 300 yards the difference between the MG151/20 and Hispano Mk II doesn't make that big if a difference, but when you get down to the muzzle velocity of the MG/FF it makes a huge difference.
All the tight clustering in the world doesn't make any difference if you're shots are almost always based on wild assed guesses. Frankly, in those circumstances a bit of dispersion might even help you get a hit by widening the cone of fire.
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but worse than engine mounted guns or fuselage guns like the Bf110, Mossie or P-38.
I remember reading somewhere that wingroot mounted guns were the ideal. The have the convergence advantage of centerline mounts without the vibration problems of engine mounts.
A centerline mount like the P38 or the Me-110 would be the ideal I think.
Crumpp
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A number of issues here.
First - gun dispersion (separated from mountings): low-velocity guns with short barrels are often very accurate - bench-rest target shooters have developed special cartridges which are much less powerful than the equivalent hunting rounds. However, high accuracy wasn't really needed in aerial combat.
Second - gun dispersion (including mountings): wing guns were known to suffer more from this than fuselage (and presumably wing-root) guns, but whether that was a bad thing or not depended....later in the war, the RAF was interested in slightly DIVERGING rather than converging the fire of their wing-mounted Hispanoes, because the inner parts of each gun's dispersion pattern would still overlap, but the wider spread would improve the hit probability. Of course, this only worked if the shells were powerful enough to inflict significant damage with few hits - it wouldn't have worked with the .50 Browning which depended on a concentration of fire.
Third - ballistics: the key is a short projectile flight time, since that minimises aiming errors both in terms of its flat trajectory and in terms of estimating the 'lead' on the target. This was achieved by a combination of a high muzzle velocity and a good ballistic coefficient. The Hispano was superior in this respect to any other 20mm cannon (with the possible exception of the Japanese Ho-3, but that saw little use).
Tony Williams: Military gun and ammunition website (http://www.quarry.nildram.co.uk) and discussion
forum (http://forums.delphiforums.com/autogun/messages/)
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Third - ballistics: the key is a short projectile flight time, since that minimises aiming errors both in terms of its flat trajectory and in terms of estimating the 'lead' on the target. This was achieved by a combination of a high muzzle velocity and a good ballistic coefficient. The Hispano was superior in this respect to any other 20mm cannon (with the possible exception of the Japanese Ho-3, but that saw little use).
Yes I am sure it was. I still don't think it will be a huge difference.
RAF was interested in slightly DIVERGING rather than converging the fire of their wing-mounted Hispanoes, because the inner parts of each gun's dispersion pattern would still overlap, but the wider spread would improve the hit probability.
I would say if your dispersion is big enough you can point your guns away from one another, the benefits of a nice flat trajectory are miniscule.
Great input Tony. Thanks.
Crumpp
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The ideal fighter weapon would be a ray gun - instant effect, with a completely flat trajectory. This would provide the greatest possible hit probability because you could always aim straight at the target without needing to estimate projectile drop with range, or the lead required when firing at an angle. So the closer you get to a ray gun - the shorter the projectile flight time, the flatter the trajectory - the better will be your hit probability.
If the ray gun had a wide cone of dispersion - but was still destructive - then it would be even better, because that would minimise the effect of any aiming errors.
It is fascinating to compare the US and German approaches to aircraft guns. The USAAF was obsessed with getting the maximum possible projectile velocity so they could get as close as possible to the 'ray gun' effect. Their experimental weapons included some .50 cals with muzzle velocities of up to 4,500 fps (compared with 2,850-2,900 for the .50 Browning). They believed that this would greatly improve the hit probability.
OTOH the Luftwaffe - which had tried the small-calibre/high-velocity route with the 15mm MG 151 - came to the conclusion that it was worth giving up something in hit probability in order to achieve much greater effectiveness when you did hit.
Which was best would of course depend to some extent on the circumstances; for long-range or sharp deflection shooting the ray-gun route does indeed maximise your hit probability - but because (other things being equal) the projectiles will be smaller and less effective, you have to hit with more of them. And in practice, most kills seems to have been made - even by the USAAF - at relatively short ranges and from more or less directly behind. In these circumstances, the lower-velocity cannon was definitely superior.
With the Hispano, you did get something of the best of both worlds - a velocity and therefore hit probability not far short of the .50 Browning's, with destructiveness comparable with the MG 151/20.
Tony Williams
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With the Hispano, you did get something of the best of both worlds - a velocity and therefore hit probability not far short of the .50 Browning's, with destructiveness comparable with the MG 151/20.
The ballistics chart is going to be key.
It is fascinating to compare the US and German approaches to aircraft guns.
Definately.
With the Hispano, you did get something of the best of both worlds
So in effect you could say the RAF had the best approach.
Crumpp
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Just check his webpage Crumpp
http://www.quarry.nildram.co.uk/ideal.htm
The Guns
The main restriction is that we can only choose technology which was in use at the time - no revolvers or rotaries! There was still a considerable choice in gun mechanisms, but of course we would only be interested in the most successful, by which I mean the ones which could deliver a high rate of fire with reasonable weight. The guns would of course be belt-fed. They should also have electrical ignition to facilitate synchronisation.
In 20mm weapons, the best performers were the Soviet gas-operated ShVAK (800 rpm, 42 kg) and Berezin (800 rpm, 25 kg), the recoil-operated Japanese Ho-5 (850 rpm, 35-37 kg) and the hybrid (gas-unlocked delayed blowback) Hispano Mk V and US M3 (750 rpm, 42 kg). The recoil-operated MG 151 could also manage 700-750 rpm from 42 kg, but the Hispano could be speeded up significantly; Molins demonstrated a version firing at 1,000 rpm, but it was not produced because too many parts were different. The Ho-5 was basically a copy of the Browning M2, which also demonstrated its ability to be speeded up, to 1,200 rpm in the M3 version. So our best choice of action seems to lie between the Hispano and the Browning.
The Hispano was a slim gun, well suited to engine mounting. As used in WW2, it fired from a rear sear (open bolt) and could not be synchronised, but electric priming would resolve this problem. The Browning receiver was relatively bulky by comparison, a problem in larger calibres. The Browning was significantly more reliable, but it appears that it relied on some high-stress components in the mechanism (which is why the Japanese had to reduce the power of the larger versions) and it may be significant that despite experimenting with various types of aircraft gun, the Americans never seem to have considered developing a version of the Browning with a calibre larger than 12.7mm. There also seemed to be problems with synchronising the big Browning (its rate of fire dropped by around 30-50%) and it is not clear that electric priming would have resolved them. The best choice would therefore seem to be the speeded-up electric Hispano.
Looking at the performance of the WW2 guns, it seems reasonable to expect our 20mm "electric Hispano" to be capable of firing at 750 rpm at the beginning of the war, increasing to 1,000 rpm by making detailed improvements. Our ideal gun could be shorter and lighter as well as faster-firing than the actual Hispano, as the cartridge is shorter and less powerful, so it should weigh around 35-40 kg. Overall, our 20mm gun/ammunition combination would not be radically better than the MG 151, HS 404, ShVAK or Ho-5 (given good quality steels) but would combine the best aspects of all of them.
Comparing this performance by using the Gun Power and Efficiency calculations (in the article already referred to) reveals a power factor of 325 (at 750 rpm), rising to 433 (at 1,000 rpm). This compares with 200 for the Hispano Mk.II and 250 for the Mk.V (the best of the wartime 20mm guns). The combination of advantages multiply to make this much more effective overall than any other gun in its class. Efficiency is also high; the weight (37.5 kg assumed) giving calculated figures of 8.7 rising to 11.5. This represents a considerably superior power-to-weight ratio to any actual WW2 gun except for the MK 108 at 9.7.
The 30mm cannon should use the same action. In fact, as the cartridges are little different in overall length, the bigger gun would be a similar length but somewhat fatter and heavier. The rate of fire should be 600 rpm initially, with 750 rpm available later, to provide reasonable hit probability. Extrapolation from actual guns indicates that this should have been achievable. There are no close matches with our "ideal" gun - there were very few 30mm cannon - but the closest actual match was the IJA's Browning-type Ho-155, which fired at 450-600 rpm and weighed in at 60 kg. The IJN's Oerlikon-pattern Type 2 weighed 42 kg, although it only fired at 400 rpm. The short-barrelled German MK 108 weighed 60 kg and fired at 600 rpm. On balance, a target of 60-70 kg looks entirely achievable.
Overall, we have a reasonably compact and light gun which due to its lighter shells is a bit less destructive against bombers than the MK 108 but is far better against fighters because of its much higher muzzle velocity, and is therefore a better all-round compromise. The calculations of gun power reveal figures of 620 (at 600 rpm) rising to 775. This compares with 580 for the MK 108 and 693 for the MK 103. The efficiency figures are also excellent, as would be expected: at an assumed weight of 65 kg, the scores are 9.5 rising to 11.9. This compares with 9.7 for the MK 108 and 4.9 for the MK 103.
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Overall, our 20mm gun/ammunition combination would not be radically better than the MG 151, HS 404, ShVAK or Ho-5 (given good quality steels) but would combine the best aspects of all of them.
That IMO sums up the Hispano. Not radically better but combines some good features.
Crumpp
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In my opinion it's a draw between the MG151/20 and the Hispano II. The standard weapons package on the Spit IX (2xHispano, 2xM2) weighs almost exactly the same as the weapon package on a 109G-6 with gondolas (3xMG151/20, 2xMG131).
Assuming that the Hispano and MG151/20 are equal in destructive capability, the 109 gun package is superior in firepower by as much as 30%, but the Spit package is easier to hit with at longer ranges.
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Another point to consider though, is that unlike Tony's theoretical electric Hispano, the Hispano Mk I, II and V all had much bulkier ammo than did the MG151/20. A lot more ammo for the MG151/20 can be carried in the same space that the Spitfire's 120 rounds are carried.
Given the weight and ammo differences I might very well prefer an MG151/20 armed Spitfire to a Hispano Mk II armed Spitfire.
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Tony, I would agree about the straight ray weapon as long as you can aim that accurately. So, IMO, the german aproach was far better with the exception of P38. Do you have stable guns with not so flat trajectory and not so high firing rate? No problem as far as you can use an accurately calibrated and marked gunsight you will be able to score accurate hits easily. Do you have flat trajectory high ROF guns but with high dispersion? You will be lucky scoring a single hit, at least at the spot were you were aiming.
In WW2 it was really important to be able to score accurate hits with the very first burst, most kills were achieved bouncing unaware planes, and you dont want to spray, alert the enemy with few scattered pings and risk a real fight.
I've seen lots of 109 guncam films were the 109 pilot aproach, aim, fire a pair of accurate shots, and then smoke, fire and bye bye spit or hurricane engine. if the gun, due the mountings, become a treacherous tool, ballistics will become secondary.
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Originally posted by Karnak
Given the weight and ammo differences I might very well prefer an MG151/20 armed Spitfire to a Hispano Mk II armed Spitfire.
Oh I know I would. If you throw out the Hisso's and .50 cals you could put four MG151/20's in their place for only 10 kg extra weight.
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Originally posted by GScholz
but the Spit package is easier to hit with at longer ranges.
Unless longer ranges mean 1000 yards, more than probably the effect would be just the opposite. I would like to see the cone of dispersion of hispanos mounted in spit wings firing at 500m compared with the cone of dispersion of the 151/20 at the 109 hub.
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Dispersion isn't a bad thing, you would want some dispersion, but not too much. Just enough to make a nice shotgun pattern the size of a fighter at 300 yards. Guns with no dispersion at all would be very difficult to aim, like shooting at clay pigeons with a rifle.
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Originally posted by GScholz
Dispersion isn't a bad thing,
It will depend on your gunnery skills. For lousy aimers, the more the dispersion the better, but probably they'll get few lucky and scattered pings causing little or no damage and alerting the enemy even with the very first tracer missing the target. On the other hand, if you are able to aim accurately and land the very first burst over a critical area (engine, pilot, wing root), you will get the kill. 109s were not for lousy aimers, you have a single gun and you cant count on dispersion to get some hit. But, if you have guns with little dispersion and you want more, just use a bit of rudders and joy and you will build your custom dispersion pattern even having a single gun.
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The vast majority of WWII pilots were "lousy aimers", and a single 20mm shell can down a fighter. Nowadays air-air and AAA autocannons are designed with a rather high dispersion on purpose to increase hit probability.
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Originally posted by GScholz
Oh I know I would. If you throw out the Hisso's and .50 cals you could put four MG151/20's in their place for only 10 kg extra weight.
Berezin B20 only weighed 25kg while MG151 was 42kg and still gave same or higher rpm and muzzle velocity...
So you could prolly fit 6 of those or more for less weight. In fact I think the B20 weigs less than US bowning 50cal. Imagine a mustang with 6 20mm cannon, or a thunderbolt with 8.. :)
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Originally posted by GODO
Tony, I would agree about the straight ray weapon as long as you can aim that accurately. So, IMO, the german aproach was far better with the exception of P38. Do you have stable guns with not so flat trajectory and not so high firing rate? No problem as far as you can use an accurately calibrated and marked gunsight you will be able to score accurate hits easily. Do you have flat trajectory high ROF guns but with high dispersion? You will be lucky scoring a single hit, at least at the spot were you were aiming.
In WW2 it was really important to be able to score accurate hits with the very first burst, most kills were achieved bouncing unaware planes, and you dont want to spray, alert the enemy with few scattered pings and risk a real fight.
I've seen lots of 109 guncam films were the 109 pilot aproach, aim, fire a pair of accurate shots, and then smoke, fire and bye bye spit or hurricane engine. if the gun, due the mountings, become a treacherous tool, ballistics will become secondary.
I agree that centrally-mounted guns were superior (so did many RAF officers) but that was because they avoided the harmonisation problem of wing guns, not because they had less dispersion. Or to put it another way, their dispersion was a gradual spread from the centre, not a constantly-varying 'figure of eight'.
Some dispersion is a Good Thing because it will increase the hit probability, provided that:
1. The shot pattern of a typical burst of fire is still dense enough to guarantee hits against anything caught 'in the cone' at normal combat ranges;
2. Each hit is powerful enough to be effective - i.e. from a cannon, not an MG.
The first gunsight which gave a reasonable chance of scoring hits in deflection shooting was the gyro sight which didn't enter service until 1944. Until then - and still to some extent after then - a high muzzle velocity was a great aid in scoring hits in such circumstances, and even then only the very best shooters could do it.
Of the various sources of inaccuracy to affect WW2 aircraft guns, by far the most significant (leaving aside pilot skill) was the aircraft itself - it vibrated, shook, skidded across the sky and was generally very difficult to keep aimed at the target for more than a second or so. That's partly why most experienced pilots liked to get in real close before opening fire - all sources of error were minimised then.
Rather OT but - Hurricanes and Spitfires could have carried four 20mm MG-FF cannon in the BoB instead of eight .303s, for much the same weight. They could have been much more effective as a result - discuss!
Tony Williams: Military gun and ammunition website (http://www.quarry.nildram.co.uk) and discussion
forum (http://forums.delphiforums.com/autogun/messages/)
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Originally posted by GRUNHERZ
Berezin B20 only weighed 25kg while MG151 was 42kg and still gave same or higher rpm and muzzle velocity...
So you could prolly fit 6 of those or more for less weight. In fact I think the B20 weigs less than US bowning 50cal. Imagine a mustang with 6 20mm cannon, or a thunderbolt with 8.. :)
Yes the B20 was probably the best 20mm cannon of the war, however it was also a very late war design. AFAIK the ShVak and B20 have a slightly lower muzzle velocity than the MG151/20.
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The best cannon ever for WW2 figters.. Too bad it came 40 years later.. :(
http://www.shipunov.com/eng/str/cannons/gsh301.htm
Tony isnt this one ideal as an engine cannon?
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The GSh-301 is probably the best aircraft gun ever made. It's only drawback is that it has a low barrel life.
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Tony what kind of cannon is it, what system is it, how does it operate? Can you give us more insight into the GSh-301?
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The berezin had a rof of 800rpm same as the shvak. The mg151 700-750rpm.
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The GSh-301 is fascinating because it's such an 'old-fashioned' design, a short-recoil type similar in principle to (although very different in detail from) the .50 Browning. The difference is that the design has been highly developed and refined to extract the maximum possible rate of fire - between 1,500-1,800 rpm - despite firing a very powerful 30x164 cartridge.
To put it in WW2 persepctive, it is only fractionally heavier than the MG 151/20, yet has the hitting power of FOUR 30mm MK 103 cannon (which weighed about twelve times as much). A Bf 109 with one of those firing through the prop hub would be....impressive.
Tony Williams: Military gun and ammunition website (http://www.quarry.nildram.co.uk) and discussion
forum (http://forums.delphiforums.com/autogun/messages/)
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How come the ammo feeds in all the way in the back?
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Originally posted by Wotan
The berezin had a rof of 800rpm same as the shvak. The mg151 700-750rpm.
Rof is not the same as muzzle velocity.
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Rof is not the same as muzzle velocity.
Absolutely right. ROF is not constant either. Heat, dirt, and condition of the springs/weapon, all work to vary the ROF. Some weapons vary more than others within the same design.
All are designed to fire within certain parameters. For example the M60 Machinegun had a cyclic rate of 550 rpm. Cyclic rate is simply a theoretical rate of fire assuming:
1. Unlimited supply of ammunition
2. Weapon never over heats or malfunctions
The practical rate of fire for the M60 is on the order of 100 rpm with a barrel change every 10 minutes. This is the "sustained" ROF and the weapon was designed to fire all day at this rate.
For emergency purposes you could fire 200 rpm with a barrel change every 2 minutes for no longer than 10 minutes.
Depending on the design, the practical rate of fire maybe very similar to a weapon with a much higher or lower Cyclic ROF.
Crumpp
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Originally posted by Crumpp
I think this springs from the fact that the MGFF in AH is a very very weak cannon when it should not be at all. The MG151's seem kind of weak as well.
My problem with the German 20mm is the trajectory, they seem to be about 75% the velocity of the Hispano, either that or the projectile itself suffers ballistically. If the bullet hits, I see little difference in the lethality/damage inflicted by the Hispano and the MG151/20, the FF is a little weaker IMHO. This is from years of playing and is entirely subjective, I have no hard data.
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Tony,
Firing a MG151/20 HE or MINE shell with the gun synchronized for 300 meters and a Hispano Mk II HEI synchronized for 300 meters, how different would would the positions of the shells be at if they impacted a target at 150m, 450m, 600m and 750m?
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The Hispano II HE shell only has a 7.5% higher muzzle velocity than the MG151/20 HE(M) shell, and 22.8% higher than the MG-FF/M HE(M) shell.
Hispano II HE: 860 m/sec
MG151/20 HE(M): 800 m/sec
MG-FF/M HE(M): 700 m/sec
For comparison:
M2 .50 BMG: 890 m/sec
Browning .303: 762 m/sec
MK108 30mm HE(M): 505 m/sec
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Originally posted by GScholz
The Hispano II HE shell only has a 7.5% higher muzzle velocity than the MG151/20 HE(M) shell, and 22.8% higher than the MG-FF/M HE(M) shell.
Just to clarify, I was talking about my experience in the game. I can hit relaibly with hispanos out to 700-900 meters, but have trouble adjusting to the drop in the 151 equiped rides. I can't think of how many kills I've lost at 300-400 meters seeing the shells fall underneath my target. In AH they just seem to drop, the Japanese ones do too, but not the Russian ones. Not that I am a LW conspiracy type or anything.
I found this thready to be very interesting.
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Originally posted by Karnak
Tony,
Firing a MG151/20 HE or MINE shell with the gun synchronized for 300 meters and a Hispano Mk II HEI synchronized for 300 meters, how different would would the positions of the shells be at if they impacted a target at 150m, 450m, 600m and 750m?
I don't have a trajectory diagram for the Hispano. However, the result would be affected by the postion of the sight relative to the guns. Other things being equal, the greater the vertical distance between the guns and the sights, the flatter the gun will appear to shoot.
Tony Williams: Military gun and ammunition website (http://www.quarry.nildram.co.uk) and discussion
forum (http://forums.delphiforums.com/autogun/messages/)
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Originally posted by GScholz
The Hispano II HE shell only has a 7.5% higher muzzle velocity than the MG151/20 HE(M) shell, and 22.8% higher than the MG-FF/M HE(M) shell.
Hispano II HE: 860 m/sec
MG151/20 HE(M): 800 m/sec
MG-FF/M HE(M): 700 m/sec
But you need to remember that the Hispano's shell weighed 130g, the M-Geschoss only 92g - and even the 'heavy' conventional German 20mm shell only 115-117g. And the lighter the shell, the faster it loses velocity and the more quickly the trajectory drops (other things being equal, as usual!).
Tony Williams: Military gun and ammunition website (http://www.quarry.nildram.co.uk) and discussion
forum (http://forums.delphiforums.com/autogun/messages/)
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Yes of course, but at normal firing distance, i.e. a convergence range of 200-400 meters the difference in projectile weight would have little effect. At greater ranges the difference would be more of a factor.
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GScholz,
I don't think you'd see much difference at 200 or 300 meters. By 400 meters I think noticable differences will be creeping in. By 850 meters, the longest range kill I am aware of in WWII, there would be very clear differences.
But more noticable than the drop would be the time to target. The higher muzzle velocity of the Hispano shortens the time it takes to get to the target and therefor makes mild deflection shots a bit easier. I would be very surprised if high deflection shots were any easier or harder with either gun.
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I'm amazed that after 60 years the powder didnt go bad
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Hi everyone,
Nice thread :-)
I'd say we all more or less agree on the qualitative effects.
What's difficult is reaching a reliable conclusion because it's difficult to say which effect outweighs which other effect.
I've tried to combine several factors into the sight pictures I originally posted in the parallel gunnery thread.
It might be that the MK108 dispersion as displayed below is only 50% of what it should be, I haven't yet figured that out.
So, the diagrams are more a demonstration of what we should look at before drawing conclusions.
For example, for judging the value of a flat trajectory, we should check out where the aiming point has to be for each weapon for a good hit probability at different ranges.
The surprising thing is, with the low-velocity blunt-nose low-sectional density MK108, you can just put the crosshair dead on target centre out to 500 m and expect good hits within half a fuselage diameter.
With the high-velocity, flat trajetory, wing mounted M2, there's no drop to speak of (though you have to watch out for the "rise" at 100 m! :-), but still at 500 m, aiming is tough because of the diverging bullet streams. To place the bullet stream on target, at 500 m you've to aim farther out to the side with the M2 than the bullet drops for the MK108!
(That's, as you're all aware, only for a stern attack at a target flying straight and level. But I think it's a good start for a weapons system-oriented discussion. We can add complexity later :-)
The conclusion I'd like to suggest: The benefits of a centre-line mount far outweigh the benefits of a flatter trajectory in such a situation.
If that's confirmed by an M2 vs. MK108 comparison, it will be even more obvious in a Hispano vs. MG151/20 comparison.
Regards,
Henning (HoHun)
P-47 battery:
http://www.x-plane.org/users/hohun/p47guns.gif
Nose-mounted MK108:
http://www.x-plane.org/users/hohun/nose_mk108.gif