Originally Posted by Dart
Easiest way I found to look at it.
They are all just car engines, each designed a little differently, some parts are swappable. They all do the same thing though.
Just like engines, some are ass.
V2 (M4/M16/G3/MP5) has some inherent flaws that make anything beyond a mild upgrade a potential problem.
V3 (AK/G36) is better - the motor cage ensures motor height/alignment is better protected. It's also less prone to have the front of the mechbox blow completely off in cold weather or with higher-powered springs.