chances are your friend is lying about getting it up to 650 fps, unless he has done no research and just saw a spring that shoots 650 fps that he thinks can just be run by any motor. once he pops it in, if it is an aeg this will happen: he wont even be able to shoot it because the motor will not be able to pull it. if it is a springer, this will happen: he will not be able to pull the bolt back because it would be wayyyyyyyyyyyy to heavy. if it is a gas gun, he might be able to get a special nozzel or something, but that would wear out the parts sooooooooooo fast. either way, this gun WILL be broken in less than 1000 shots, as the spring will brake all the internals.
either that, or its 650 fps with a .12 gram, and that is a little more reasonable with a sniper weight bb, joule wise. still a little hot, but not too hot to play. my friend has a 450 fps ak, and that kills, so i recommend an MED for the sniper, but thats just my opinion.