If you’re reading this, odds are good you know 5.56 is a rimless, bottlenecked cartridge developed by FN Herstal. But, you might not be as familiar with some of the military’s intricacies inside the caliber itself. I’m talking about M193 vs M855.

Militaries standardized the cartridge for NATO forces in 1980. Before that, NATO adopted the 7.62×51 in 1954.

The 5.56 is derived from the 223 Rem. The two cartridges share identical dimensions. They are not, however, interchangeable.

The power load of the 5.56 is substantially greater than that of the 223 Rem. So, 223 Rem may be fired in a weapon rated for 5.56, but never vice versa.

Types of 5.56×45 Ammunition

An AR-15 with M193 ammunition on a table

The military uses several types of 5.56 cartridges. These include the M196 and M856, which are both tracer rounds with distinctive orange tips, the M199 dummy round, the M200 blank. The military also fires M862 but they use it exclusively during training exercises.

The civilian market most commonly has access to one of two types of 5.56: M193 Ball and M855 Ball. A ton of this ammo is manufactured at the Lake City Army Ammunition Plant in Missouri.

M193 vs M855 Ammo

What is M193?

M193 ammo on a stripper clip

If you were to label any of the 5.56 cartridges “vanilla,” you would pick the M193. It is the standard cartridge the military issues for field use in the M16A1 rifle. It features a 55 grain bullet. A lead core with a full metal jacket make up this cartridge. Its muzzle velocity is 3,250 feet per second, although that speed quickly tapers off. You might also be interested to know the M193 performs poorly when asked to penetrate any kind of barrier. Because the M193’s jacketed bullet is not designed to expand during penetration, it is permissible for use in international warfare according to the rules laid out during The Hague Convention of 1899. (Please note that it is inadvisable for a civilian to conduct international warfare.)

Buy Federal XM193 Ammo here from AmmoForSale.com.

What is M855?

These are the “Green Tips” You’re Looking For

M855 green tipped ammo on a tableThe M855 (also known as an SS109 or “penetrator”) features a heavier 62 grain full metal jacketed projectile, with a seven grain steel tip which is painted green for easy identification and a spitzer boat tail. The M855 is slower than the M193 at 3,025 feet per second, although its greater sectional density and drag coefficient make it more accurate over long distances. The M855’s steel tip strengthens it considerably: Under optimal circumstances it will penetrate 15 to 20 inches into soft tissue, and also pierce 0.12 inches of steel at approximately 2,000 feet.

The M193 will reliably fragment during penetration at a velocity around 2,700 fps or faster.

The tougher M855 is less inclined to fragment than the M193. For that reason the world considers it a more humane combat cartridge. However, the M855 is capable of yawing during higher velocity penetration, during which it may fragment at the cannelure.  (Yawing is when the bullet’s rotation starts to stray away from the path of flight. You’ll hear shooters refer to this sideways turn as “tumbling” quite frequently.)

Fragmentation transfers greater energy within the target than if the bullet had merely passed through, a consideration if you would implement either M193 or M855 for self-defense.

The M855 has by no means a magical bullet that is capable of boring through any barrier. Our troops in Iraq frequently found the M855 insufficient to penetrate auto glass, even at close range, and the bullet’s ability to puncture steel drops markedly at the 1,000 foot mark. At approximately 1,650 feet the M855 ceases to be practical for engaging a specific target.

Buy Federal 5.56×45 M855 ammo here at AmmoForSale.com.

Totally Mil-Spec, Right?

The bullet of M855 vs M193 bullets

Note: while a cartridge may be accurately designated as M193 or M855, almost all commercially available 5.56 ammunition is not technically mil-spec.

Federal indicates this by adding an “X” prefix before a round’s designation. Other manufacturers may omit the distinction entirely. The difference between a 5.56 round that is mil-spec and one that isn’t is generally so minute that it is moot. Manufacturers produce the ammo to such tight tolerances civilian shooters likely won’t notice any difference.

When To Use M193 or M855

Also note that the relatively long M855 projectile will work well in a 1:7 twist barrel, but will likely incur performance problems in 1:9 twist or 1:12 twist barrels. The M193 is less sensitive to barrel twist, but may present issues when fired from a barrel with a slower twist.

We are very fortunate to have access to so many manufacturers’ offerings in both M193 and M855. The only true way of discerning which side you’re on in the M193 vs M855 debate is through healthy experimentation. So, get ready for some range time.

We can say though – if penetration is your priority you would most certainly be happier with a magazine full of M855 cartridges.