M3 Barrel Extension Browning Machine Gun Parts Search for: Search 600978 Shank, Barrel Extension, M2HB. $49.95 7191302 Breech Lock, Late, M2HB. $49.95 6008784 Pin, Breech Lock, M2HB. $8.95 731211 Barrel Extension, M3. $399.95 6008908 Spring, Lock, Barrel, M3. $12.95