Okay so yesterday some friends and I decided to shoot AR's. My friend pulled his out and proceeded to load a mag up sat down at the bench to shoot and his rifle wouldn't pick-up the rounds he would pull the charging handle back load one round it would fire and then CLICK! it did this all day, its not the ammo or mags as we tried those in different guns and both were fine. So my question is does anyone have any insight as to what it might be, his gun is a bushy M4A3 with a CAA 6 pos. stock and everything else is factory assembled ant help would be greatly appreciated.