About WW2 fighter aircraft firing power

[Stewart]

Infact I agree with you that the USAF might have done better by adopting a cannon like the Hispano or the MG 151. However, it's not the point discused here. I dispute this idea! That the USAF shot down many more Axis planes than any of, or possably all of the other Allied powers is not open to dispute! Given that the allies planes all had about the same performance Vs their Axis opponents, yet scored so much better, both in absolute numbers and as a ratio of the number of missions representing opportunity.
That the Germans chose to use guns not well suited to shooting fighter planes, but which were much better at bombers is a politicle desision.

[George Hopp]

2. Increase the rate at which projectiles are fired by increasing the number of guns or speeding up their rate of fire (N.B. The Luftwaffe preferred to fit 2x low-velocity 30mm MK 108 rather than 1x high-velocity 30mm MK 103 for the same weight, because the MK 108 combo put shells into the air at three times the rate). However, that requires a bigger ammo capacity and more weight again.

The Germans at Tarnewitz compared the two weapons in a report dated 7.9.43. They concluded several things:

1. For the weapon + mounting + accessories + ammunition for 20 sec. firing, the MK 103 weighed 259kg (taking a volume of .29m cubed space) and the MK 108, 214kg (volume, .10m cubed space).

2. They noted that that between 400m and 1000m,
with an attack from directly behind the MK 108 would score more hits.
with an attack at 15 degrees deflection, both cannon would score the same number of hits.
with an attack at 60 degrees deflection, the MK 103 would score more hits.
But, if two MK 108s were installed, weighing 428kg and taking up .20m cubed space, vs. the MK 103's 259kg and .29 m cubed space, the twin MK 108 armament would be more powerful than that of the single MK 103 under all circumstances.

3. While the MK 103 had a greater vo: 900m/s vs the MK 108's 525 m/s; it also had a far lower firing rate: 380/min vs. the MK 108's 680/min.

All the above data is from the report.