The one thing I dislike about the M4 and M16 is the handgrip at the front. But I guess with a rail system and a vert grip it'll be different. So tuning up to 400 fps is generally not that great of an idea? I know that the higher FPS you go the more likely it is to strip a gear or ruin a piston or spring or whatever isn't reinforced. So saying that - a stock gun shooting about 300 FPS should really only be tuned up to like 350-380 tops?
Also, I already said I was going to the LZ to rent and play and get age verified. So no worries about that, all these questions are for future reference if I get sucked into the sport - which I know I will.