Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: Imowface on March 06, 2011, 10:16:36 PM
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Was having a bit of an argument the other day on 200, explaning to people that the NS37 could make acurate shots at super long ranges so I did some pictures for them to show how the bullets dropped and spread at various ranges
(http://www.mediafire.com/imgbnc.php/d32636d3f602e6ce9d356080809fde806a3c1a96f7b60b9a62ff998c7fce5e416g.jpg)
(http://www.mediafire.com/imgbnc.php/18dbb6552f43f21b230dade1cd0e8349b71c26a765c6ecae81ae0d4e9209fe1a6g.jpg)
(http://www.mediafire.com/imgbnc.php/a7cb441d7bb51e954faadbc7445d8bbd01bf9ec20ca2692a860a3463309be0ff6g.jpg)
(http://www.mediafire.com/imgbnc.php/1891de3de6f4d84afa755cd24744b39464d2666cb686837855046f010bae00666g.jpg)
(http://www.mediafire.com/imgbnc.php/dc044fb850077954888d6e8babf5144166868807c1fd851b39d534bdbd8baa776g.jpg)
you will notice that there are alot more bullet holes then what the 9t carrys for ammo, I had set it to unlimited ammo in offline to test rapid fire, and just using single shots,
I hope these pictures help people see how great the NS37 is, and that if you can get used to it, the slow rate of fire does not effect you vs fighters.
Disclamer for these tests my convergance was set to 400, the reason I have it set close is that I have found in the MA that 650 may lead to problems hitting things up close around 200, as you have to aim low at that point
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its insainly accurate. . .and why are you on 200 arguing with some of these people anyway. . .bombing run in a 29?
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Heck it isnt! just ask my 262 haha
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Now in offline mode film shooting at cons with one shot only trigger taps. Watch how many hit but do no serious damage. Watch how close your shots come to the con but slip past. Repeat with the K4 one shot taps with the MK108. Fewer miss and more cause damage when they explode. It has seriously bad dispersion values in real life. Play your film back at x.08 to see all of this. NS-37 shoots like a lazer with minimum dispersion.
You will note that getting an explosion against the base of a fighter's rudder with the NS-37 has no effect. You have to weave from side to side and hit the upper part of the rudder from the side. Repeat this exercise but with an M3 on the runway. NS-37 slaughters the M3 and the MK108 takes a few rounds. NS-37 is alergic to aluminium.
In air to air with the NS-37, seems like you need a double or triple tap to kill things. At least offline in the pattern. The NS-37 HE round is the same as the Russian M1939 37mm manned ack HE round for killing aircraft. Should perform those one hit kills that our manned feild guns do. Single hit flash and the fighter falls to the ground.....
Playback at x.08 is long and tiresome. But, you will see some interesting things if you place your self just to the front side and above the target con and watch the rounds in slow-mo zoomed a bit as they come in from behind. Look for the round that hits dead center of the rudder's trailing edge and how neatly the tracer splits in half as the trailing edge cuts it in half. Saw those most often against K4 and G14 in the traffic pattern offline.
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I have always maintained that the YAK-9T's 37mm is like a damn Laser...case in point, happened awhile ago but had a 38 BnZ me, miss, I hit rudder, pulled up and at 800 fired 1 37mm with the pipper just a tad above 38s nose in climb. 38 went poof and I went home happy. Great weapon!
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Now in offline mode film shooting at cons with one shot only trigger taps. Watch how many hit but do no serious damage. Watch how close your shots come to the con but slip past. Repeat with the K4 one shot taps with the MK108. Fewer miss and more cause damage when they explode. It has seriously bad dispersion values in real life. Play your film back at x.08 to see all of this. NS-37 shoots like a lazer with minimum dispersion.
You will note that getting an explosion against the base of a fighter's rudder with the NS-37 has no effect. You have to weave from side to side and hit the upper part of the rudder from the side. Repeat this exercise but with an M3 on the runway. NS-37 slaughters the M3 and the MK108 takes a few rounds. NS-37 is alergic to aluminium.
In air to air with the NS-37, seems like you need a double or triple tap to kill things. At least offline in the pattern. The NS-37 HE round is the same as the Russian M1939 37mm manned ack HE round for killing aircraft. Should perform those one hit kills that our manned feild guns do. Single hit flash and the fighter falls to the ground.....
Playback at x.08 is long and tiresome. But, you will see some interesting things if you place your self just to the front side and above the target con and watch the rounds in slow-mo zoomed a bit as they come in from behind. Look for the round that hits dead center of the rudder's trailing edge and how neatly the tracer splits in half as the trailing edge cuts it in half. Saw those most often against K4 and G14 in the traffic pattern offline.
I've been saying something isn't right with the NS-37 for years. It doesn't seem to cause damage a portion of the time. On some airframes (the 38 in particular) it gets great results with a hit. On others, (Lancaster, P51) only certain shots get good damage. I've hit a spit 16 4 times in the same wing and had it fly away fine. Do that in a .303 armed bird, and the wing falls off.
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I've been saying something isn't right with the NS-37 for years. It doesn't seem to cause damage a portion of the time. On some airframes (the 38 in particular) it gets great results with a hit. On others, (Lancaster, P51) only certain shots get good damage. I've hit a spit 16 4 times in the same wing and had it fly away fine. Do that in a .303 armed bird, and the wing falls off.
I get the same feeling that the NS-37 HE is not on par with the mk108...hard to get any proofs
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I have never had a shot not kill a plane smaller then a heavy bomber, poof or no poof a ping still rips a wing off or explodes him
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It seems counter intuitive while talking about this. We all agree that 880M/sec makes the NS-37 shoot like a lazer versus 500M/sec. But be honest. Have you ever gone offline and tested both cannon with single shots? Or if you have, did you hit the trigger and it was 2 or more got out then kaboom?
Fly the offline pattern and tap only a single round at a time from 200 while filming it. Say a minimum of 10 sec between shots to stay honest. I got more MK108 single tap kills/hits than NS-37 and the NS-37 shoots like a LAZER.... It's a long and boring procedure. But the slow motion(x.08) film playback is interesting. Just remember the NS-37 puts out 2 with tracer and one invisible. The invisible one makes you think the con does a delayed explosion or is so damaged by the previous hits that it blows up with a tracer passing next to its skin.
Yes if you double or triple burst per trigger pull with the NS-37 at 200 your chances of a single round hit is good. But, you can single round hit at will with the MK108 and it does not shoot like a lazer. Try the M4/37 in the P39. Funny how it single shots a lot like the MK108....
If I post my films it can reasonably be argued my results are due to my eye/hand specific coordination. If this audience each goes to the trouble of performing this testing then we have a tad more scientific set of observations to compaire.
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you have to remember, this isnt about anything more then the fact that it is possible to accuratly shoot to 1000 yards with this gun
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I started out testing the NS-37 from the accuracy premise.
The physical results could not be ignored since the one shot issue is so intriguing. You are aware your dipersion value at 1000 is 70 feet left to right? Target=180ft, 9 rings 10ft wide. Thats not accurate at all even with an almost 40ft drop value. At 400 your dispersion is 20ft and at 200 5-10ft. But, your drop stays inside of 10ft 200-400 which makes the apperence of aiming dead on. Land and air engagement distances in russian testing of the NS-37 started at 400m and closer. In game thats suicide against a wirbel.
Try the MK108 at 650. You have to aim high by almost 50 mil because the drop is about 2x of the NS-37 at 1000. But, the dispersion is about the same picture as your 1000yd screen for a barrel only 23 inches long opposed to a nearly 6 foot barrel on the NS-37.
I just keep reminding myself this is a computer game and not the Anthony Chabot firing range near my house where my lookup tables from Hornady, Hodgon and Sierra make sense versus my target results.
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I just keep reminding myself this is a computer game and not the Anthony Chabot firing range near my house where my lookup tables from Hornady, Hodgon and Sierra make sense versus my target results.
.... never mind... stupid error on my part, wrong window
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As far as I'm aware, there is no inherent characteristic of barrel length that affects dispersion.
If both weapon mounts are stable, the dispersion would come down to some characteristic of the projectile.
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"As far as I'm aware, there is no inherent characteristic of barrel length that affects dispersion."
AFAIK there is, especially in aircraft use. While a long barrel is better in providing flatter flight trajectory and higher MV it is also more susceptible to translate vibrations to dispersion, either airframe related or results from rapid firing.
Just a clarification if people tend to think that eg. MK108 is more inaccurate than Hisso 404 due to much shorter barrel. Physically it is not but due to other characteristics it is harder to gain hits with MK108 at long ranges so the choice to use a longer barrel starts to make sense despite worse dispersion.
-C+
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Wasn't it the MK 108 that went to a shorter barrel during development, due to some issue specifically with the original longer barrel?
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Charge,
You are absolutely right. I should have been more clear and said there is no reason a shorter barrel would cause more dispersion.
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"As far as I'm aware, there is no inherent characteristic of barrel length that affects dispersion."
If dispersion is to be considered the impact spread of multiple projectiles fired separately at the same target over a given period of time then the above statement would seem incorrect. When it comes to firearms. The shorter the barrel the less accurate the weapon. The longer the barrel (provided it is a rifled barrel) the more stability that is imparted upon the projectile. I haven't done enough smooth bore shooting of different length barrels to say its the same deal for smooth bores but I suspect it is. If the commenter was referring to multiple projectiles fired simultaneously like a shotgun firing birdshot then the term "dispersion" takes on added dynamics.
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The barrel must be long enough to enable the bullet to acquire its max rotation velocity. Beyond that longer barrel does not help. I am sure there is some rule of thumb for this, something like 1.5 rotations or so. For higher muzzle velocity rifles, the barrel needs to be longer if the desired rotation rate is the same (the bullet moves more in the time it takes to complete the 1.5 rotations or whatever number),
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Physics-wise, longer barrels impart more force on the round as the gasses push the round down the barrel.
This means faster velocity and better ballistics. The Mk108 has a terribly short barrel and that is one reason for the very slow velocity and weak ballistics. The NS37 has a long barrel and very flat trajectory thanks to its much faster speed.
Now it's not always a matter of making barrels longer or shorter. The recoil of the cartridge into the spring is what helps reload and recock the gun, and unless the timing is perfect you can mess things up. You need the bullet to exit the barrel as the next shell is being readied. That means if you take an existing designe and lengthen the barrel you need to make the spring stronger so the recoild keeps those gasses in play longer. You cannot load the next round with gasses still pushing a round down the tube, and you can't load and fire another with the first still firing.
It's all very interconnected and complex, but generally as a rule of thumb the longer the barrel the better the velocity and therefore the flatter the trajectory.
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Longer barrels give the propellant gases more time to act on the projectile. If the barrel is too long, the extra friction can actually slow the projectile down.
The Mk108 does have a slow muzzle velocity and that would lead to a lot of drop, but not 'dispersion'.
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Longer barrels give the propellant gases more time to act on the projectile. If the barrel is too long, the extra friction can actually slow the projectile down.
The Mk108 does have a slow muzzle velocity and that would lead to a lot of drop, but not 'dispersion'.
Like I mentioned it's all interconnected... You need the larger powder charge and the stronger springs for the longer barrels, and you're right after a certain point that does happen...
But you have to make it pretty long for that to happen.
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Yea, it would have to be real long for that to happen.
I guess if the barrel wasn't long enough to get the projectile to a stable spin rate that could lead to all kinds of bad things, but then you'd get bullets flying backwards and sideways and stuff. Not just a big pattern.
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You forget that the barrel design itself can also lend to accuracy or not.... B-25 strafers would fire until their barrels were white hot, and then keep firing. They liked the scatter gun effect as the barrels lost accuracy.
So low tolerances, or just different designs, different grooves (more twists, less twists, etc?) can all come into play.
EDIT: As well as projectile shape itself... Look at the major improvements when they added the boat tail to rifle rounds. Then look at a German MG151/20 round. Flat, squared off almost.
There are many reasons something may or may not be "accurate"... and then something may be "accurate" while having poor performance, or be a great performer but have terrible consistency. Also the "cone of fire" does reflect actual WW2 specs. The guns flexed, the mounts flexed, even when stationary tested on the ground, Bf109Es had a "cone of dispersion" for both MGs and MG/FF cannons. You got as much of the bullet holes into the zone as you could. They didn't all fall into the same bullet hole.
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The barrel length doesn't play into the accuracy equation all that much, as long as it's within acceptable limits.
Regardless of barrel length, the "fit" of the projectile to the inside of the barrel matters a ton, and not all barrels are equal. A short barrel can easily prove more accurate than a long barrel. Another deciding factor is the overall length of the cartridge, and how close the bullet sits to the back of the rifling.
Cartridges are purposely sized a bit "small" so that they're sure to fit in the variably-sized chambers (due to tolerances, and often differing manufacturers) they're designed for. As a result, two things happen. First, the cartridge sits tipped "nose-down" a bit, resulting in it hitting the rear of the rifling at an angle, deforming the projectile. Second, the projectile actually moves forward a bit before it engages the rifling, again resulting in hitting at a slight angle, and deforming the projectile. That effects accuracy. And it can effect it a lot.
The action itself effects accuracy as well. A less-rigid action is generally less accurate than a more-rigid action. And then there's the rifling. Projectiles are stabilized by RPM, not by how many inches they travel per revolution. That means the projectile velocity needs to be matched to the degree of rifling.
The cartridge itself- how consistent are the rounds loaded. What are the tolerances for powder weight? How consistent is the powder composition? Possible air pockets in the projectile, effecting overall weight and balance? Are the rounds consistent enough to result in the same velocity? What's the range of velocities?
There are more factors than that of course, but it's a start...
The barrel length is just one little variable.
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Yea, it would have to be real long for that to happen.
I guess if the barrel wasn't long enough to get the projectile to a stable spin rate that could lead to all kinds of bad things, but then you'd get bullets flying backwards and sideways and stuff. Not just a big pattern.
Pardon my french but- natura non facit saltus - there ought to be be an intermediate "big pattern" regime between flying sideways and high enough speeds that the rounds' dispersion due to insufficient spin/speed/etc are negligible.
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Difference from RL is that we shoot at distances fighter vs fighter off angle at 600 yards, whereas a shooting distance of 250 would be more normal.
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Moot,
I'm definately not a small arms or direct fire expert, but the way I see it there are only a couple factors that come into play at ranges that are as short as what we have in AH.
One factor is muzzle velocity. Obviously, the faster a projectile is moving, the faster it will get to whomever it is going to hit (our or limit of ~1.4/1.7k). The quicker it gets there the less time gravity has to act on it, so the less it drops. From our point of view, these bullets 'fly straighter' (.50s, Hispanos). This has absolutely nothing to do with dispersion. Dispersion can be thought of as the variation in impact point of a group of rounds about the mean for the group.
There are different things that cause dispersion. Obviously if the projectiles are different in some way this will cause a great deal of dispersion. Another factor is flexing in the gun mount or the barrel. Another significant factor is little changes in met conditions along the trajectory - these cannot be controlled for and will always exist and the best way to 'counter' them is to have a high MV so that the met has a little time to effect the projectile as possible.
If I had to guess, I'd say that HT went with a model that assumes these factors are the same for all guns and mounts, and that the quality control guys at the factory were doing there jobs so that the projectiles are all functionally identical (within type - so a 20mm MG 151 projectile will fly the same as any other 20mm MG 151 projectile. This leaves random disperion, which is either a constant for all projectiles, or varies so that the higher the MV the tighter the pattern.
There might be some difference in dispersion between ground mounts, fixed air mounts, and flexible air mounts but that can be tested.
Actually all of it can be tested, I just don't have the desire :)
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So you're saying that projectiles shapes (from projectile type to type, not within a type) and their various velocities combined are a non factor in dispersion?
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Well dispersion is the measured variance from the mean point of impact for a given group of rounds. There would be an impact if we were shooting different projectiles in a given belt, but all the rounds in AH are an amalgam of the different kinds of projectiles (for example HE AP Mine) in a belt so there aren't different shapes.
The shape of a projectile impacts the drag, which effects the amount of drop, but it wouldn't effect the dispersion.
How you want to model it depends on how accurate it needs to be. For AH purposes, a simple point mass system is close enough with some randomness thrown in - basically you could just wrap up everything that causes dispersion into a fudge factor or two.
One factor would be easiest, but I'd go with two - one for met and one for 'everything else' (gun mount rigidity, barrel flexing, minute differences between projectiles) because the muzzle velocity would tend to decrease the dispersion due to met (which is mainly due to changing wind conditions - not a big factor anyway over the ranges we are talking about).
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What I was thinking, and I'm at least as much of a layman on this, is that some rounds' shape could be more susceptible to tumble, or something. I wasn't thinking of it in principle as the discussion has bent towards, but in terms of the difference between NS37 and MK108. Maybe the 108 had a combo of projectile shape and too little barrel to result in more dispersion. Or maybe HTC based the difference in dispersion on historical data..
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What I was thinking, and I'm at least as much of a layman on this, is that some rounds' shape could be more susceptible to tumble, or something. I wasn't thinking of it in principle as the discussion has bent towards, but in terms of the difference between NS37 and MK108. Maybe the 108 had a combo of projectile shape and too little barrel to result in more dispersion. Or maybe HTC based the difference in dispersion on historical data..
I think your last statement is probably correct. There's data to support modeling a "generic" dispersion for a given gun.
It's not a "too little barrel" issue. It really doesn't take much barrel to stabilize a round. As an example, I have a flintlock dueling pistol with a rifled 10" barrel that shoots three shots into a 1" group at 50 yards. That's about the max I've tried, due to the sights, but knowing what I do about stability there's no reason to suspect the projectile would lose stability beyond that range.
Tumble---
When it comes to stability, the actual RPM (and its resulting gyroscopic forces) of the rotating projectile is the critical factor (and it's controlled by velocity and rifling). Let's assume a round is fired at 100yds, out of a barrel that is rifled to cause the projectile to rotate once every 18". No matter what the velocity of the projectile is, the projectile will rotate twice every three feet traveled, so will rotate 200 times in its 300ft flight. Now, let's assume one shot is fired at 1000fps, while another shot is fired at 500fps. In both cases the bullet will spin 200 times before it hits the target, but... the RPM of the faster-flying bullet is twice that of the slower bullet. It hits the target quicker, so squeezes those 200 revolutions into a smaller time-period.
When it comes to shape... You're right, some shapes are more prone to tumbling, which is why the RPM is adjusted through velocity and rifling. The most stable shape for a projectile is a ball. It can be stabilized at slow velocity and with a slow rate of twist. As an example, my .54 muzzle-loader only uses a 1-70" rate of twist (the ball rotates once in 70" of travel), and doesn't require a high velocity to stabilize the ball. However, a ball is a terrible shape to resist drag and maintain velocity because it presents to much frontal (and rear) area to the slipstream, making it a very high-drag shape.
To decrease drag, bullets are elongated to present less frontal area with a similar (or even greater) mass. The problem with that is that as a projectile gets longer in relation to its diameter it gets less stable (more likely to tumble). This longer bullet will require a higher RPM to stabilize. That can be done by either increasing the rate of rifling twist in the barrel, or by increasing the velocity (more powder, or a different powder, or both) or by increasing both.
To make it more complicated, the overall diameter of the projectile dictates the required RPM as well (i.e a .32 round ball needs to spin faster than a .54 round ball to remain stable. Same shape, but a different RPM requirement). A smaller diameter projectile needs a faster rate-of twist.
Compare those numbers to modern center-fire barrels which generally have rifling between 1-10" and 1-14", and often a much higher velocity as well (resulting in a much higher RPM.
What this eventually leads to is a "best" round for a given barrel. A round that delivers the proper velocity to result in the proper RPM for that bullet, out of that barrel.
Vibration-
This can actually lead to a lot of "dispersion", even without any "outside" influence from the engine, etc. When a gun is fired, it creates vibration in the barrel. This vibration will alter depending on the bullet weight and powder charge, among other things. This vibration leads to the muzzle vibrating. Imagine the muzzle vibrating left/right or up/down, or a combination of both. The timing of when the projectile leaves the muzzle is at play here. If the rounds leave while the muzzle is in vibratory transit from left to right, you'll get more dispersion. If the timing is "perfect" and the round leaves when the muzzle momentarily pauses at the right or left before reversing direction, you'll get less dispersion. It sounds crazy, but explains why one brand of factory-spec ammo will fire large, ineffective groups out of a barrel, while a different brand will fire much tighter groups. The "sound" is different, resulting in a differetn vibration, and a different time-of-exit for the projectile. Even changing the projectile within the same brand matters (or can).
And in the end, it means that once a "best" round is found, other rounds fired out of the same barrel aren't as good. This is one reason why tracer rounds may not fly like non-tracer rounds, etc... It also means that less-stringent tolerances results in greater dispersion (or can). Maybe two rounds have precisely the same amount of powder, and precisely-matched bullets. What if the composition of the powder isn't identical? Or what if one bullet has an off-center air bubble within it? What if two barrels are made by two different manufacturer's (or by the same one) and aren't exactly identical? Do they fire the same bullet to the same place? Not usually...
Range-
The RPM of the projectile doesn't slow at anywhere near the rate that the overall velocity of the round slows. That means that the projectile doesn't lose stability as quickly as it loses effectiveness. When it loses 1/2 of its forward speed, it has not lost 1/2 of its stability.
All those things, and more, contribute to dispersal. Most are "nit-picky" for airplane guns, so probably weren't really worried about (and probably still aren't) which just leads to more dispersal in the end...
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Thanks MtnMan. Especially the bit about charges' sound. That makes a lot of sense, I'd never thought of it.
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I'm not sure many associated with this game have seen the document linked below.
The MK108 had a 1:16 twist in a 23inch barrel to impart a high rate of spin to unlock the fuse on a 150mm long round. Yes a 3cm ball vs 150mmx3cm would be very stable from a 23inch barrel 1:16 at 500m/sec.
Page 11 shows a parabolic dispersion curve. Values are meters in radius. Tests from a bench, not a moving aircraft. If those values are the average spiraling corkscrew path of the MK108 round from a test bench, you cannot hit much of anything past 25-50 meters very often in G force affected flight manuvering. 100 foot wingspan level slow moving bombers past 50 meters possibly?
On page 10 is also data from a MK103 which might infer an aproximation of how the NS-37 HE round at 860M/sec might perform. MK108 data at 500m/sec is on page 10.
http://deutscheluftwaffe.de/archiv/Dokumente/ABC/m/MK%20108/Text/Munition/Daten%20Bleatter/Datenbleatter.pdf
Good explanation of how the centrifugal fuze works.
http://www.xs4all.nl/~robdebie/me163/weapons15.htm
The AZ1587 throws a single ball bering to one side off center to unlock the fuze. A possibility of wabble?. The ZZ1589 uses multiple ball berings.
If you look at this description for a practice round, how many real rounds had the same problem due to natural instabilities during combat.
Type G, German name: unknown
Tar-filled practice mineshell with an unbalance stick for short range. Pressed and rolled steel body with an steel dummy fuze and an steel unbalance stick. The unbalance stick is bent outward on the top causing the shell to fall into unbalance shortly after leaving the barrel and thereby greatly reducing the range of the shell. Weight of shell: appr. 330 +/- 8 grams. Shell probably of experimental design.
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I have not seen it said in this thread, and only HT/Pyro could say for absolute certainty.
But I suspect the difference buster is seeing in hits doing major damage is that the N-37 is loaded with a significant portion of AP ammo. Where the 30mm is all HE.
That is in my opinion why the Yak9T and the iL2 do so well against ground targets.
And can seem to do not as well vs air targets.
So some of those hits with the 37mm are punching right through, not exploding.
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But I suspect the difference buster is seeing in hits doing major damage is that the N-37 is loaded with a significant portion of AP ammo. Where the 30mm is all HE.
That is in my opinion why the Yak9T and the iL2 do so well against ground targets.
And can seem to do not as well vs air targets.
The YakT has entirely different ammo in game than the IL 2 - That's why it's actually doing much worse against armored ground targets. With an IL-2, a few hits vs top armor will take out a Tiger, a yak-t can shoot away all day even with hundreds of rounds (tested offline via ammo multiplier)
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I have not seen it said in this thread, and only HT/Pyro could say for absolute certainty.
But I suspect the difference buster is seeing in hits doing major damage is that the N-37 is loaded with a significant portion of AP ammo. Where the 30mm is all HE.
That is in my opinion why the Yak9T and the iL2 do so well against ground targets.
And can seem to do not as well vs air targets.
So some of those hits with the 37mm are punching right through, not exploding.
HUH? Yak9T NS-37 is HE only. And it's absolutely horrible with GV's other than soft skins.
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Would any of this audience like to comment on the page 11 parabolic dispersion curve for the MK108?
http://deutscheluftwaffe.de/archiv/Dokumente/ABC/m/MK%20108/Text/Munition/Daten%20Bleatter/Datenbleatter.pdf
If this dispersion chart is correct, our MK108 shoots like a slow lazer or the M4/37 in our P39Q which has aproximently a 6ft barrel 1:16 twist and initial velocity of 610M/sec. The NS-37 barrel is 7.8ft 1:16 twist, 870-900M/sec.
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NS-37
The two basic types of projectiles were:
OFZ, High Explosive Incendiary, weight 735 grams, muzzle speed 890 mps.
BT, Armor piercing with tracer, 753 grams. Ballistic cap, without any kind of incendiary or explosive filling. Muzzle velocity 870 m/s.
Penetration 48 mm high strenght steel at 300 meters ( 20 º angle)
Testing with the OFZ showed it could explosively "shatter" 18mm rolled plate steel. It's not punching holes in aircraft. If it hits the aircraft, it should fall apart the same way our manned ack gun performs a one shot kill. We don't have the earlier german tank versions with thinner armor in the game which the Lagg3 with the Shpitalny Sh-37 could defeat. At the Battel of Stalingrad Lagg3 escorted by Yak were effective bomber killers. The rounds used in the Sh-37 are the same as the NS-37. Our german half track, M8, M3, LVT and jeep are vulnerable to the OFZ round. Our aluminum skinned aircraft in the game seem to be coated with "OFZ Begon".........
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I love attacking wirbs and ostis in my Yak9T weaving in and out of trees. Most AAA peeps never study that little area between the treetops and the ground :)
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Barrel length is matched with the burning speed of the cartridge to get the most out of it.
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icepac,
Unfortunatly the short barrel length in the case of the MK108 was not matched to the powder. It was so that max pressure was never reached helping with the low recoil while getting just enough spin induced to unlock the fuse. Unlike the NS-37's recoil by the third round fired raising the nose of the Yak9T off target, the MK108 had relatively littel influence on the attiude of the aircraft.
The document I posted is from Rheinmetall-Borsig's testing of their gun and ammunition. Page 11 of the document shows a parabolic dispersion graph that never shows up in the Rechlin Erprobungsstelle Bordwaffen document most players on the internet can download freely. You can search around for a free download of Borwaffenmunition.pdf. The MK108 in game looks like it uses the ballistic data table from this document.
The Rechlin document is a compilation of manufacters testing documents. You will notice on page 35 for the MK108 500M/sec data Rechlin only includes a column for "Strich" with the "Sütterlin" capitol letter D for dispersion. If you were Rechlin and wanted the explosive power and low recoil of the MK108 but had to sell Berlin on the gun with a short effective range and crappy dispersion value, which value would you sell as the dispersion at 100 meters?
Rheinmetall-Borsig's - A 6 inch drop and roughly anywhere in a 28 foot circle at 100 meters due to parabolic dispersion.
Rechlin E'stelle - A 6 inch drop with a 7 foot dispersion at 100 meters.
Now if anyone on this forum can determin another meaning for the page 11 parabolic dispersion graph data please do so.