Originally Posted by highny
And could you change an m4 into a m16 and reverce?
Yes you could, but it would not be an economical solution for more airsofters.
Just visually, you'd need a complete M4 and M16 upper receiver and a collaspible and a fixed stock. You could swap the upper reciever parts and have only one upper body, if you had lots of time on your hands. It's not something that you would really be able to do easily in the field. Internally, you'd there's quite a few changesto the cylinder and the wiring. Again, you could modify it to work but one or the other version would suffer from poor performance somewhere because of it.
Realistically, unless you built the crap out of the M4, the M16 might get about 20'-30' more range, tops. If you're talking a stock gun, it's probably less that a 20' advantage for the M16.