Carbine length ar-15 are generally over-gassed, and that can increase reliability if your firearm is dirty and can also cause increased parts wear throughout the gun's time as well as increased felt recoil. The Gorilla H buffer helps to soften the recoil impulse of your rifle by slowing down the bolt action cycle, while getting back on target quicker without affecting reliability. While the buffer is heavier and slows down the action, it increases dwell time that helps to keep your gun from getting dirty while improving the lifespan of your firearm parts. Choosing the correct buffer weight is a balance is an act between gas system , barrel length, and ammo. One of the general rules is to inspect your expended brass. If it is being ejected at 1 , 2 or 3 O'clock,, if that's the case your system may be over-gassed, and theGorilla H buffer is the upgrade you are looking for.