I actually stayed away from M4 style ARs because I had read that they extracted more violently. My understanding was that the M4 has a barrel length of 14.5" and that the gas system is 7" long and this works great. But, when ARs get made for the civilian market manufactures use a 16" barrel, but still have a 7" long gas system. So, what happens is the bullet is still in the barrel as the gas is hitting the gas key and opening the bolt. So, the pressure of the gas in the barrel violently blows the bolt carrier back. Which means the extractor spring and the components get the piss beat out of them, or something to that effect. Am I correct? Also I read that a midlength gas system is 9" long and works the best for a 16" barrel. Basically my understanding is that the bullet has to be out of the barrel so the pressure in the barrel drops just before the action opens, otherwise the bcg is going to be blown back violently. I appreciate any comments Wanna kill these ads? We can help!