Angstadt Arms Buffer kit, .40/.45 AR Pistols, 8 oz Buffer, Buffer Spacer and Buffer Spring, Anodized Black Finish AA45BUFKIT The Angstadt Arms 9mm heavy buffer assembly kit is compatible with blowback AR-9 style firearms chambered in 9mm" 40S and W and 45ACP. Includes 8oz solid state buffer and carbine buffer spring.