I stopped by the LGS looking for a heavy buffer for my Rock River. When I told the employee I was looking for 1 to smooth out the recoil I was told all I needed was a different spring. He then told me that the heavy buffers were for rifles not carbines. All this while holding a carbine heavy buffer. I may be new to ARs but I do know the differece between carbine and rifle buffers. This is the same guy who once told me not to buy ammo from Walmart due to expiring primers. I did not buy the buffer from him, wanted as much for an unknown buffer as a Spikes H2. On the plus side he did GIVE me a carbine length spring so now I have an extra. I think I've made my last trip to that store!