Check out this video of the first live fire of the General Dynamics GAU-22/A four-barrel 25mm cannon onboard an F-35 Joint Strike Fighter at Edwards Air Force Base in California. It weights in at 230 pounds and spits rounds out at 3300 shots per minute with a muzzle velocity of 3560 feet per second. Here’s a pretty interesting tidbit, what if you need to take out bad guys while taxiing?!
The tests are done using a target practice round, PGU-23/U, which fires from the gun, but does not explode on impact.
The tricky part about this test phase is that the gun will never operationally fire on the ground. To conduct the test, they have to use software to bypass interlocks and “fool the aircraft to make it think it’s in the air.