5.56 55GR PMC FMJ-BT (556X)5. 56 55GR PMC FMJ BT (556X) is part of the PMC X TAC line of ammunition, tried and tested by military and law enforcement around the world. Manufactured to the high standards and specifications required by these organizations, X TAC is the choice for the professional and enthusiast alike. Quantity 100 rounds 1000 rounds (20 rounds per box, 50 boxes case) Manufacturer PMCBullet Weight 55 grainBullet Type FMJ BTMuzzle Velocity 3120 fpsCasing Brass