US ww2 issue 20mm HE VS: 55gal. empty oil drum

[GODO]

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.

[Karnak]

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.

[Crumpp]

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

[Karnak]

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.

[Crumpp]

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

[GODO]

"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.

[Karnak]

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.

[Crumpp]

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

[Tony Williams]

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 and discussion
forum

[Crumpp]

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

[Tony Williams]

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

[Crumpp]

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

[Wotan]

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.

[Crumpp]

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

[GScholz]

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.