Attempting to crimp a brittle frangible bullet into the cartridge case may break the bullet. Frangible bullets striking animal targets create wounds similar to conventional bullets. During penetration, a frangible projectile's core fragments into many high-velocity pieces. The shooter used hollow-point or frangible bullets which increase tissue damage. Frangible bullets disintegrating in flesh cause very serious wounds with persistent effects. Hard targets may be damaged by frangible bullets. The last category of expanding bullets is frangible bullets. Most frangible bullets are subject to brittle failure upon striking a hard target. Fragmenting bullets should not be confused with frangible bullets (see below). Each bolt had a nut at each end, the top one being a frangible nut. A frangible joint is a structural separation system that is initiated using ordnance. Special frangible rounds made of a lead/Bakelite combination were developed that would disintegrate upon impact. The frangible nut was captured in a blast container. These were known as the "Cartridge, Caliber .30, Frangible, Ball, M22". In September 1942 the United States standardized them as the M1 Frangible Grenade series.