the idea behind magnetically fired projectiles is to surpass the velocity limitation of expanding gas wich is somewhere around 5000 fps. for some reason, useing an idea designed to propel an object 5000+ fps to fire a paint round at 300 fps seems messed up to me, besides, the only way you could work the power source small enough would be to use some pretty kickin capacitors, like a couple farads worth, and they would have a brutally long charge time between each shot fired, nobody will take a gun onto the field that has a rate of fire thats counted per minute, this is a game of seconds and fractions there of.
If your body is really wierd, try showing it to people in the streets for money.-Hitchhikers Guide to the Galaxy, Tips for aliens in New York, Surviving