5.56 Ammo Guide: M855 vs M193

5.56 Ammo Guide: M855 vs M193
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5.56 Ammo Guide: M855 vs M193

How to choose between these two common, and classic, loads

When shopping for 5.56mm ammunition M855 and M193 are sure to land on the potential “buy” list. Both of these popular loads have one small issue, but several things going for them.

The good news is they are often the cheapest ammunition available and M855 adheres to military specifications, which can be beneficial. Here’s how to tell exactly what you’re buying.

M855 and Green Tip Ammo

M855 is only loaded at the military’s Lake City ammunition factory. If you see “M855” on the box, it’s the same stuff that our military issues and it comes with all of those features.

The bullet is a 62-grain projectile that has a lead core and steel penetrator in the nose, all wrapped in a copper jacket with a dab of green paint on top.

Buying ammunition marked “Green Tip” might mean it has the same bullet, but it won’t have the rest of the M855 features.    

M855 is designed for use in M-4 and M16 rifles, as well as open-bolt belt-fed machine guns. Almost all these firearms are fully automatic.

The military made a wise decision in specifying that the primers for M855 be “staked” or “crimped”, meaning some of the brass on the case head around the primer is pushed over the edge of the primer to physically lock it in place.

This makes reloading difficult, but it’s a great call when weapon reliability is paramount.

M855 vs. M193 5.56 Ammo

 Why Primers Come Loose in AR-15 Rifles

Shoot enough rounds through an AR-15, M-4, or M-16 and you’ll have a primer fall out the back end of the cartridge case.

The rifle still has residual chamber pressure when the bolt unlocks to extract and eject the round. The puff of smoke that comes out of the ejection port is visual proof of residual chamber pressure.

What that means is there is still pressure inside the case when the bolt moves rearward. This pressure helps unseat the primer and, when the case mouth clears the ejection port, allows the primer to fall into the trigger group.

All M855 ammunition has staked primers to prevent this from happening.

The other unique feature that M855 has is sealant around the case neck. Pull any bullet from an M855 round and you’ll find a black ring around the bullet’s bearing surface.

That’s sealant, specified by the military, to prevent moisture intrusion into the powder column. There’s also a dab around the primer for the same reason.

Sealant is hugely beneficial if storing ammunition in areas that are not climate controlled, especially with high humidity. No ammunition stores with less fuss and better than M855.

How M193 Differs From M855?

M193 is the other military-issued load, but there are some key differences between it an M855.

While they share the same crimped or staked primer, M193 does not have any sealant present because it was not a requirement when the specifications were written. Nobody thought to put sealant on cartridge cases back then.

The other significant difference between the two is the bullet. M193 uses a 55-grain, lead core, full metal jacket projectile.

Neither this bullet nor the 62-grain M855 bullet are going to give great accuracy, but both make good plinking ammunition and can be used for self-defense.

When used for self-defense, M855 has better penetration, especially when shooting through intermediate barriers. M193 bullets do a better job of fragmenting once they’ve impacted the target due to the entire core consisting of soft lead.

How About XM193?

M855 is a known commodity that is only produced at Lake City, and M193 is produced there as well.

If you ever run across XM193 when shopping for ammunition, it is similar but not the same thing as M193.

XM193 probably won’t have a staked primer and it won’t have to pass the same quality control specifications that M193 will.

Neither commercially sold M855 or M193 actually pass these military specifications, but it’s loaded with the exact same components on the exact same lines.

It just doesn’t get tested before shipping like the actual military stuff does.  

M855 and M193 are great choices when you want a lot of ammunition at a low price. They are also high-quality choices, with M855 offering some unique weather-proofing features that make it great for long-term storage.

Just don’t expect tight groups.

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ronald thomas
good article on m855 and m193 ,now what round gives a tight group