If the hammer is down and I put the gun on safety and try and work the bolt it will not cock all the way back unless I really rack it hard.   (Basically the gun wont cock when its on safe)   I have two m4s and the one with the stock trigger guard does not do this, only the one that has the A&S trigger guard installed does.   I've compared both side by side to see what was going on and here is the scoop..   On the A&S trigger guard, when the bolt is in the process of cocking