Is there a diffrence? I have been told there is no diffrence. I have problems with my AR failing to feed on occassion. the problem isnt always there but when it is there it does not go away throughout the shooting session. Last weekend I shot a 30 rd mag just fine and after that it FTF every time. the bolt was not traveling back far enough to feed the round on every shot. I have been shooting 223 but the gun is rated for 5.56. cant find 5.56 at any LGS. Is it the ammo or the firearm?