Algodoo

This is a thoroughbred machine gun built using Roast Beef's gas feedback method. This is probably the highest fire rate you're going to get out of a clip fed gun using spring bullets.

I cheated a little bit! The simulation frequency is 350. In order to reset your sim frequency to normal press "P" while the sim is running after you're done playing with the gun.

I spent almost 4 hours building and tweaking this gun. No matter how much tweaking I did though, I couldn't get a fire rate that was much faster than my "Flak Cannon" scene which was made in beta 5.25. With the increased frequency I was able to get the most out of the gun, so no complaining

Enter = Fire
up/down = aim
P = reset sim frequency

360 rounds per minute (only six rounds though)