What is the biggest cannon that would fit in a P39 nose? (1 Viewer)

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The P-39/M-9 combo woul've been about the only one tank buster that could take care about itself. Or P-63/M-9, for 1944 and later.

The M10 was a 'better M4', our Charles Bronson has articles covering the cannons in the 'Armament' subforum.
 
".... The P-39/M-9 combo would've been about the only one tank buster that could take care about itself. Or P-63/M-9, for 1944 and later. "

Given the appropriate AP ammo .... which the Americans did not supply to the Soviets, IIRC. :)

MM
 
M4 M10 cannons (a real P-39/P63 cannon) were using lower power cartridge (610 ms), cmopared with M9's 900 m/s muzzle velocity. M10 was not in service with any P-39/P-63 unit, IIRC.
You're right about USA not supplying AP ammo to Soviets.

Perhaps RAF might've installed the Hurri IID cannon in P-39s - that one was somewhere in between of US guns power-wise, closer to the more powerful M9.
 
I read the UK had a 40mm canon that mite work.

Yep, the Vickers' Class 'S', the one mounted at Hurricane IID.

I've seen a lot about it being a very good anti-aircraft weapon but I'm sure I've seen comment that said its low muzzle velocity 'drop' made it poor against ground targets?

That would be the MK 108; MK 103 was the real powerful one.
 
The Vickers S gun is just a prewar 2-pdr surveyed for an aerial mount, it's rebuilt for the role but basically right off British Cruiser tank. It's a lot more like a battlefield improvisation than a purpose built aero gun. Same deal with the Tetsefly's 57mm, which is right off a British MBT, it's the 6-pdr gun with most of the barrel chopped off.

I'd go with the a purpose designed aero gun from the ground up if I could. Less likely to have unforseen complications in service. What's the ammo on S-guns, 12-rd externally loaded clips? You don't want to be much further away than about 10km from the airfield to the battlefront.
 
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Actually the Vickers S gun used the Britishs 2pdr pom pom AA gun ammunition. but a different mechanism. A 158mm long case rather than a 304mm long one.

The Tetsefly's 57mm did not have it's barrel chopped. most of the gun was inside the plane. Cutting the barrel lowers the velocity of the shell and since the energy is proportional to the square of the speed cutting barrels of anti-tank (or anti armor ) weapons is counter productive.
 
How well would the MK-108 do with a longer barrel.

Not much. Barrel length has to matched to the amount of propellant and it's burning rate to get the the best performance. A longer barrel could have added a few hundred FPS to the MK-108 but since it is starting out at about 1700-1800fps that sin't ging to get it to the 2500-2900fps range of many other cannon.

There is a reason that the MK 101/MK103 used a cartridge case over twice as long as the MK 108 used. It held a LOT more powder.


see: Komet weapons: MK 108 cannon
 
Actually, with a longer barrel i think the weapon would suffer catastrophic damage after the first round.
 
You might be right. One reason for the short barrel was so that the shell would clear the barrel and allow the pressure to drop before the breechblock moved back too far. If the breech opens too soon the unsupported case will blow out and allow high pressure gas into the action. A jam at best and a damaged gun very likely. If the escaping gas cooks of the next round in the feed things could get VERY messy. A heavier breech block and stronger main spring would solve this but then the cycle rate goes down. Aircraft guns, for all their size and power, were a delicate balance.
 
Even the ground-based cannons rarely got a longer barrel without a whole different cartridge is used.
German 5cmL60 used bigger cartridge than L42, the 7,5cmL70 vs. -43/-48, 8,8L71 vs. L56 etc.

Here is how the weapon bay looked like; the M4 seems like a tight fit length-wise. The another picture can help to put the space between front part of the beams in scale.
 

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