To be honest these are great guns, yes the internals are dated, fps is a little lower as a result, & the fire rate is a little slower,
BUT
The bodies are solid & realistic against real steel, the fire rate is also close to real steel as well (the pig was never meant to be a sewing machine), so for realism it's spot on, would make a great working prop for themed games, or even for vehicle mounting, just don't plan to chuck 10k bbs in a single game.
The only mod I made to mine was to convert a 249 powered box mag & stick it in an m60 box mag pouch, worked great.