Alternative airborne guns

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The 'big Besa' that is sought-after by friends and foe alike might've perhaps looked like one of these two suggestions:
- It is designed around a 20mm cartridge, that is powerful as, say, MG 151/20 or maybe the Oerlikon FFL - good payload and MV, not too heavy, belt-fed from day one.
- Czechs design a 'mid-power' 15mm cartridge - instead the 75g shot @880 m/s, the MV is at 730-750 m/s. Not going overboard with cartridge power (it was more powerful than German 15mm) should mean the weapon is much lighter and smaller. Granted, this will push the weapon more towards the airborne use, rather than to AA and AT use the Czechs were trying to get with the historical ZB-60.
 
The 'Tetse' Mosquito used a 57mm 6 Pounder gun in the Mosquito in a quasi AP role to penetrate submarine hulls even below the waterline. Given the greatly superior accuracy of the 40mm S Gun on the Hurricane over the 60 lb rocket projectile might the 75mm version (ROF QF75mm) using HE not be useful against and targets? The cartridge case is the same size. Only the shell is larger so the stresses should not be grossly different to the normal Molins Gun.
 
The British 75mm tank gun used the same ammo as the US 75mm guns as used in the Sherman tank, which is also the same ammo as used by the gun in the B-25s.

Recoil is going to go up, recoil is dependent on momentum and not energy.

While the 57mm is often described as being bored out to take 75mm ammo there was a bit more to it than that.


2nd round is the 57mm (with APDS shot) 3rd round is the 75mm. The 57mm is actually about 3mm bigger across the rim.
 
Yes, rechambered as well as made with a larger bore and the extra mass of the larger shell will add to the recoil forces but HE is less dense than steel shot so the difference may not be too much. The Molins did not use APDS but solid shot.
 
Hey guys,

These are the Muzzle Energy (ME) values for the UK 6pdr and US 75mm AP solid shot. The 6pdr Mk II gun is the short barrel AT/Tank model. The 75mm M2 is the gun mounted on the M3 Lee/Grant tank, and the 75mm M3 is the gun on the M4 Sherman. ME is in long tons (2240 lbs).

6pdr AP shot = 306 ft-ton (Mk II gun, 6.28 lbs at 2650 ft/sec)

75mm AP shot = 349 ft-ton (M2 gun, 14.7 lbs at 1850 ft/sec)

75mm AP shot = 464 ft-ton (M3 gun, 14.7 lbs at 2030 ft/sec)
 
For recoil just multiply the projectile weight times the velocity. Then divide the number by the weight of the gun. That will give you the velocity of the gun.

This does not include the weight of the propellant or the velocity of the gas ( which is more of a constant regardless of the velocity of the projectile.) It also takes no account of the recoil mechanism and how it distributes the recoil load over time.

The U.S. and British 75mms ammo used very similar AP and HE projectile weights and velocities so they could use the same aiming marks.
 
Hey Shortround6,

I used ft-tons ME because it is a commonly used way of expressing the amount of energy that a cannon size projectile has when leaving the muzzle. The value ft-tons for larger guns (and ft-lbs for small arms) when used to express the ME is a way of saying how much work has to be done to reduce the projectile velocity to 0. This is also equal to the total amount of work necessary to reduce the recoiling gun barrel (in a fixed mount) to a velocity of 0, even if you do not know the weight of the gun. This means that, everything else being equal, the cannon with the higher ME will require the mounting structure and aircraft structure (since that is what we are talking about here) to be stronger in proportion to the increase in ME, so the structure(s) can absorb the recoil energy without failing.

Obviously, you can use different mechanisms to reduce the stress on the structure(s), such as redirect some of the gas energy that would otherwise result in rearward movement (ie muzzle break). Or allow the work done in slowing down the gun to occur over a longer period of time (longer recoil mechanism), as long as the methods are compatible with the installation.

Although you can figure the velocity of the recoiling gun using the method you mention above, it is the work equivalent of kinetic energy that is required to stop the gun. In physics Work equals Kinetic Energy (W = KE).

Incidentally, for anyone not already familiar with the matter, if you double the velocity of a given projectile it does not take 2x the work to reduce its velocity to 0, it takes 4x the work. It will also take 4x the work to reduce the velocity of the recoiling cannon barrel to 0, and the mounting and (local) aircraft structure will have to be able to absorb the same amount of energy.

Anyway, for the 6pdr and 75mm guns mentioned above, the 6pdr Mk II is (I think) the AT gun comparable to the Molins gun, and the 75mm M3 is (I think) the comparable tank gun to the 75mm used in the B-25 gunships. So the 75mm will require a structure capable of absorbing approximately 1.5x the energy of the 6pdr. That might be too much for the Mosquito, at least in a practical sense.
 
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Actually , once you have figured out the velocity of the recoilling gun you can figure out the energy of the recoiling gun.

However the Muzzle energy comparison only works for guns that either have similar velocities (and then not real well) or similar weight projectiles.

As an illustration consider the 220 Swift with a 48 grain bullet at about 4000 fps and a 45/70 with a 405 grain bullet at just under 1400fps fired out of similar weight guns (or 12 gauge shot gun slugs) going by memory the 220 Swift has about 1600 ft lbs of ME beating the heavy bullet guns. But it sure kicks a lot less

However rifles do not have recoil mechanisms that, while they don't eliminate recoil, they spread the load over time (distance) which reduces the peak loads on the structure.
Same cannon allowed to recoil 12 inches or allowed to recoil 36 inches, which puts a much larger strain on the structure?
 
Let's give the Oerlikon FFL a greater prominence. France, UK and USA make a deal with Oerlikon for that gun by mid-1930s, erstwhile in the drum-fed version. The belt-feed version is introduced some time in 1938/39 perhaps. The FFL, vs FFF and FFS, was in-between with regard to weight, RoF and muzzle energy. It was not a featherweight as the FFL, but with 35-38kg it was no heavyweight either. MV, for the 127-128g shell, was a bit under 700 m/s in early versions, while the Japanese versions gotten a bit more than 700 m/s (they also introduced the belt-feed of their own making in service).
What this can gain for the UK & USA is again mostly related to the crucial feature - timing. There is no need to juggle too much between the shell weight and MV as in case of the FFF derivatives. Ammo is slender (and a bit lighter than of the historical Hispano), so more can be crammed in same volume.
By mid-war, the main improvement should be increasing the rate of fire, 500 rd/min is not awe-inspiring by that time. Japanese managed to improve the RoF to 675-750 rd/min by 1945 (they introduced their version of the FFL in late 1942/early 1943 in service).
A lot of the data for this is taken from Tony WIlliams' article: link

For the Soviets: the 'ShKAS-20' - the known ShKAS LMG up-sized for the 20mm cartridge. 1000++ rd/min?
 
- Adopt the MG210 to supersede the 151, using the same ammunition - 15mm or 20mm. The 210 was designed by Mauser to do just that, employing gas in place of recoil operation. Rof 1000 vs 700 rpm, weight 32 vs 42 kg, power/weight ratio 1.875 times better (and iirc about 300mm shorter).
- For a 'mid power' cannon, neck the 20mm MG213A cartridge out to 24 mm for a ~200 g M-shell, m/v ~850 m/s. Fire it from a 213A, weight ~55 kg, rof reduced from 1100 rpm (20mm) to say 900-950 for reliability. Fit four in the Me 262 in the lower nose , two with their ammo tanks each side of the nosewheel well. That would make room for an extra fuel tank above if you want. Use it also as a centreline prop cannon and try out synchronised in the wingroots of the Fw 190 and Ta152.
 
Could continued development of the 40mm S Gun (as used on the Hurricane IID and IV) have kept it viable in an AT role? Obviously not to penetrate the frontal armour of a Tiger II tank but an aeroplane can choose it's direction of attack. The majority of german armour was more lightly armoured than the Tiger II anyway. Early MkIVs could be penetrated in all directions by land 2 Pounders in 1941 tests and a, for example, Littlejohn equipped @ pounder with the additional airspeed of the aeroplane will far exceed that. So was it the RPs being more versatile, the Hurricanes suffering too many low level AA losses or the weapon itself being too weak? It was certainly far more accurate than RPs.
 

Littlejohn adapter for the S gun was tested, with favorable results.
link
 
yulzari said:
land 2 Pounders in 1941 tests
Click to expand...

Land 2 pounder used a different cartridge case and projectile.

From Anthony Williams website.
The 40 X 158R is the Vickers S gun cartridge (and 2pdr AA gun) while the 40 x 304R is the "land" 2pdr. The 40 X 311R is the 40mm Bofors gun of WW II.

You could probably do a fair number on a Panther tank from the side and rear using the Vickers S gun with standard ammo . Tiger I (forget the II) would be a very tough target even for the Little John ammo.
 
fastmongrel said:
The problem with the Little John is you're stuck firing AP. Hurricane IIDs operating outside of the desert usually fired HE. You can take the Little John off but then the sights need adjustment.
Click to expand...

Yulzari specifically asked for improvement of armor piercing capability. Littlejohn adapter and ammo is a step in that direction.
There is a lot of bomb- and/or rocket-firing Hurricanes around.
 
Tweaks for the Germans:
- MK 108 that fires a 250 g M-shell at 600-650 m/s instead of the 330g one at 500 m/s
- MK 108 necked-down to 25mm; 200g M-shell at ~700 m/s?
- MK 103 firing a long, 400g M-shell at ~750 m/s instead of 330g M-shell at 860 m/s
- MK 103 firing a down-loaded 330g shell at 700-750 m/s, so the recoil can be mild enough for Fw 190 to carry & used two such guns
 
tomo pauk said:
MK 108 that fires a 250 g M-shell at 600-650 m/s instead of the 330g one at 500 m/s
Click to expand...
This might not be much of an advantage.
For a give stage of fuse development you can't make the fuse lighter so that means you cut the body of shell and the HE capacity more than the 75-76% indicated.
The 30mm mine shell already lost velocity at a pretty alarming rate. A shorter, stumpier projectile will loose velocity even faster so you may not get much, if any, increase in practical range. That is much difference in time of flight to a given/desired range.
 
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