Spike's Tactical ST-9X Heavy Buffer, 9mm, Fits AR-15 Rifles, Stainless Finish SLA009X Spike's Tactical stainless steel heavy buffer for use in a carbine stock. The ST-9X is a dedicated 9mm buffer due to its extended length. Its extended length helps eliminate the problem of breaking bolt catches. The buffer will smooth the gun out" make it more reliable and decrease the amount of gas in your face when shooting suppressed.