On 14/07/2020 10:49, The Natural Philosopher wrote:

Test showed that to e.g. break a main spar of an enemy fighter with 303
ammunition needed a LOT of hits.

Also spitfires were not stable gun platforms - the wings would twist
under recoil. Hence lots of guns, and eventually lots of guns up closer.

This was apparently the main reason why the 12-gun Spitfire wasn't
proceeded with - the deflection of the wings throwing the outer guns
somewhat off aim.

4 x 50 cals would have been better, but they were not reliable. The 20mm
cannon was.

Not in 1940...

There was an issue with the HS404 that meant that in combat the guns
could misfire. The official view was that the rounds were being too
lightly struck by the (fairly light) bolt, the solution being to machine
1/16th or so from the face of the receiver, so that the bolt would be
travelling faster and make a misfire less likely. When that was done,
stoppages reduced to an acceptable level.

--
Spike