FWIW, the buffer does do several things. It adds mass to the bolt carrier group, and adds an element of adjustability, with the 3 weights inside of either steel or tungsten (heavier). A standard carbine buffer has 3 steel; an H1 has 2 steel and 1 tungsten; an H2 has 1 steel and 2 tungsten; H3 has 3 tungsten. The spring is what absorbs the energy of the rearward motion of the bolt carrier and buffer, and returns them forward into battery. The "loose" weights in the buffer give a "dead blow" effect going into battery to reduce the possibility of the bolt "bouncing" back out of battery. This is helpful in full auto guns; probably not absolutely necessary in semi-auto guns. Adding weight to the buffer slightly delays the bolt unlocking, slows the velocity of the BCG, and therefore delays ejection slightly. Unless the gas port is a bit large and the gun is "overgassed" (and most are, at least slightly) a carbine buffer should work fine. If the gun is functioning 100% and you're getting ejected empties 5-8' away and somewhere between 2 and 3 o'clock, I wouldn't mess with it. If all the brass is banging off the deflector and landing at 1 o'clock, you may want to add some weight. An H1 or H2 also may soften the felt recoil a little, and move the ejection more toward 4 o'clock, but you risk losing some reliability if the gun gets dirty or perhaps in cold weather.