Rate of Fire

[Hilmar]

I built some files of modern guns and placed them into a fighter, but the M-61A1 Vulcan only fired at 20 round per second - it should be 100. Why it doesn't work?
To test the file, I set the rate to 10/15/20/40/60/100, the 600 rounds are enough for 60/40/30/30/30/30 seconds. There is a limit, but I can not find the reason.
Who can help?