The Angstadt Arms 9mm heavy buffer assembly kit is compatible with blowback AR-9 style firearms chambered in 9mm" 40S&W and 45ACP. Includes 8oz solid state buffer and carbine buffer spring.Features : Complete drop-in 9mm AR-15 buffer kit Compatible with 9mm, 40S&W and 45ACP 8oz buffer weight Includes buffer and carbine spring