Machined aluminum recoil buffer comes in three weights, so you can select the buffer that gives the best combination of recoil control and reliability in your carbine with an M4-type adjustable stock. All have a mil-spec polyurethane bumper, durable hard-anodized finish, and the Spike's logo. ST-T1 is a standard-weight (3 oz.) buffer filled with low-density tungsten powder (LDTP) that eliminates the noise and shock caused by the hard reciprocating weights found in the original-style factory buffer. Aids in smoother cycling and helps minimize bolt bounce. ST-T2 is filled with high-density tungsten powder (HDTP) for extra weight (4.1 oz.) behind the carrier to reduce cycle rate. Help you Mfg: Spikes Tactical SPECS: Aluminum, hardcoat anodized, black. Polyurethane bumper. 3¼" (8.2cm) long. ST-T1 3 oz. (85g) wt.; ST-T2 - 4.1 oz. (117g) wt.; ST-T3 5.4 oz. (153g) wt. Fits AR-15 carbines with M4-type collapsible stock only.