Winchester(R) White Box is the ultimate in budget-friendly performance and reliability. These rounds feature the iconic M193 55-grain Full Metal Jacket projectile. PLEASE NOTE: While the 5.56x45mm round will fit in a .223 Remington chamber, 5.56 is a military round that is loaded to higher pressure than its .223 counterpart, and is therefore not recommended for use in rifles chambered for .223.