First Breach 5.56 NATO 55 Grain Full Metal Jacket Boattail New C220 Brass Cased Rifle Ammo 20 Rounds 556 55 loaded. 56 NATO 55 grain match-grade ammunition. FB USA .223REM Headstamp. Specifications for First Breach 5.56 NATO 55 Grain Full Metal Jacket Boattail New C220 Brass Cased Rifle Ammunition: Manufacturer: First Breach Caliber: 5.56x45mm NATO Number of Rounds: 20 Bullet Type: Full Metal Jacket (FMJ) Bullet Weight: 55 grain Cartridge Case Material: Brass Package Contents: First Breach 5.56 NATO 55 Grain Full Metal Jacket Boattail New C220 Brass Cased Rifle Ammunition Ammunition Tray First Breach 556 55 loaded: 5.56 NATO 55 Grain Full Metal Jacket Boattail New C220 Brass Cased Rifle Ammo 20 Rounds