First Breach 5.56 NATO 55 Grain Full Metal Jacket Boattail New C220 Brass Cased Rifle Ammo 1000 Rounds. 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 - Bulk: Manufacturer: First Breach Caliber: 5.56x45mm NATO Number of Rounds: 1000 Bullet Type: Full Metal Jacket Boat Tail (FMJBT) Bullet Weight: 55 grain Cartridge Case Material: Brass Muzzle Velocity: 3250 ft/s Package Type: Box Primer Style: Centerfire Package Contents: First Breach 5.56 NATO 55 Grain Full Metal Jacket Boattail New C220 Brass Cased Rifle Ammunition - Bulk Loose rounds in sealed packaging First Breach 50009: 5.56 NATO 55 Grain Full Metal Jacket Boattail New C220 Brass Cased Rifle Ammo 1000 Rounds