This is a Angstadt Arms Kit known as the Buffer & Spring, model AA45BUFKIT.
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
