This is a Luth-AR Buffer, model BS-11C.
Luth-AR's Standard .223/5.56 Carbine Buffer Body contains 3 steel slugs in the buffer for a total weight of 3.2 oz. or .20 lbs. The standard weight AR-15 Buffer provides reliable function with rifle length gas system rifles.
Features:
Standard .223/5.56 Carbine Buffer
Standard weight AR-15 buffer
