The Difference Between M855 5.56mm 62 Grain Steel Core and 5.56 62 Grain FMJ-BT
Ammunition comes in many different forms whether it be different calibers or different projectiles within calibers. In this review, we will discuss the difference between the 5.56mm M855 62-grain steel core and the 5.56mm 62-grain FMJ-BT. Both are 5.56, the difference lies within the projectile.
M855 refers to the classic military “green tip” ammo than many veterans are familiar with. There are often misconceptions with steel core ammo. The M855 ammunition is NOT armor-piercing ammo. It does, however, have a steel tip in order to penetrate more effectively than soft-tipped ammunition. Steel core ammunition has a small steel projectile surrounded by softer lead. This generally increases the prices of this ammunition to that of ammunition with projectiles composed solely of lead.
FMJ-BT referring to ‘Full Metal Jacket - Boat Tail’
Full metal jacket ammunition has a lead core that is fully encased in copper or another harder metal. The “boat tail” refers to the tapered back of the projectile, the part that seats into the casing. This tapered design makes FMJ-BT much easier to load, making them cheaper and more popular. The tapered back end makes loading easier and reduces the chance for knicks and chips on the projectile when it’s loaded. Imperfections in the projectile can greatly reduce accuracy.
Which is better?
It depends on what you are aiming to accomplish. For most applications, FMJ-BT is the cheaper and more common round. M855 is banned on many shooting ranges due to its steel tip. M855 is also more expensive and can be harder on your rifle than FMJ ammo. The only real disadvantage for FMJ-BT is its possible over penetration. The round fires with such velocity and penetrates so effectively that it can pass through its target and hit something behind it. But as long as you’re aware of this you can mitigate its effect. “Wouldn’t M855 have a higher likelihood of over penetrating than FMJ-BT??)