I remember one of them in the '80s that fired an 11 oz Lexan projectile with a muzzle velocity of 14,000 mph.
(that's 4,812.5 gr at 20533.33 fps)
Of course, the rails had to be replaced every other shot, and the SWITCH to activate it had to be replaced every shot.
I wonder what happened to the compulsator-powered 9 MJ coil gun the Army was testing back in the '90s? We never heard anything about the results... (Yeah, the Army was looking at slinging them on tanks... the size shells they were looking at, 'point blank' range would be out to the horizon!)