Quote:
Originally Posted by Triggaaar
That's interesting, thanks. It can't be easy to get the damage model from bullets right, in real life if a pilot could still fly home after being shot, they would. In IL2, we'll keep going unless we're on fire (time to rtb  ). Cannons obviously do more damage but bullets were still very effective. Both sides were choosing to use bullets at the end of the war when they could have used cannons exclusively if they'd preferred.
Is there any documentation on why they added cannon to the Spitfire, but kept machine guns too (whether they just thought cannons were better, or if the cannons were primarily for shooting bombers)?
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In general, both sides wished to replace machine guns with cannon wherever possible. USN studies showed that one Hispano cannon has firepower equivalent to 3-3.5 .50cal Browning MGs. The Hispano's rate of fire and muzzle velocity are only marginally lower than the Browning M2, making it an excellent weapon with a great balance of ease of use vs damage.
However, in certain cases it wasn't possible. Spitfires for example retained MGs even after the C Wing versions could be fitted with 4 cannon, because there were issues with the outer guns freezing up at high altitude. Eventually they did switch to full cannon armament for the MK21, but this saw only very limited service before the war ended.
US attempts to use the 20mm Hispano were thwarted by their redesigning the gun in an attempt to make it conform to American manufacturing standards. The resulting version had an extended chamber, which caused rounds to misfire, and was also prone to jamming when fitted in wing mountings (although it worked reasonably well when fitted in fuselage mountings, since these suffer less from vibration). Despite the manufacture of large quantities of both guns and ammuntion, the problems were not resolved until near the war, at which point the change would only have caused disruption.