US Cartridge, 75mm APC-T, M61A1
This projectile, as its name indicates, is an armor piercing round.
This projectile has a 7.5 caliber radius of ogive, a gilding metal rotating band, a fringing groove, a single groove for stab crimping, and a square base. The body of the projectile is of hardened forged steel. A cavity machined in the base contains the explosive filler which consists of 0.15 pound of Explosive D. To the nose of the body is crimped and soldered an armor-piercing cap, which is centrally hardened and peripherally toughened. This armor piercing cap is designed to take up the initial shock of impact, thereby protecting the body, and to set up favorable stresses in the plate, so as to enhance penetration by the body itself. It also reduces greatly the possibilities of ricochet on highly angled impacts.
Collaborative Ordnance Data Repository