5.56 NATO Ammo Guide: Loads, Rifles and What We Stock

This 5.56 NATO ammo guide covers what the cartridge is, how the common military-style loads differ, which barrels they suit, and what we keep on the shelf at our Phoenix warehouse. Every load named here is one we stock by the case. Each product page shows a live count and a 360-degree spin of the actual box we ship.

What 5.56x45mm NATO is

5.56x45mm NATO is the military rifle cartridge of the M16 and M4 family, standardized across NATO in the early 1980s. It has nearly the same outside dimensions as the commercial .223 Remington, but it is loaded to higher pressure and fired from a chamber with a longer throat, or leade. A rifle marked 5.56 NATO can fire both 5.56 and .223. A rifle marked only .223 Remington should be fed .223 unless its maker approves 5.56. The .223 Wylde chamber, common on AR-15 barrels, is built to handle both. Our 5.56 vs .223 answer covers chamber markings in more detail.

Most 5.56 loads use bullets from 55 to 77 grains. Military-style ball ammunition comes in two main types. M193 is a 55 grain lead-core full metal jacket. M855, called SS109 in NATO paperwork, is a 62 grain full metal jacket with a small steel penetrator ahead of a lead core, and US-made M855 carries a green-painted tip. From a 20-inch barrel both leave the muzzle at roughly 3,000 feet per second or a little more. A 16-inch carbine gives up some velocity.

Twist rate and bullet weight

Barrel twist decides which bullet weights fly straight. A 1:7 or 1:8 twist, standard on most current AR-15 barrels, handles everything from 55 to 77 grains. A 1:9 barrel is usually fine with 55 and 62 grain loads. Older 1:12 barrels, found on some early rifles and varmint guns, are meant for 55 grain and lighter and may tumble a 62 grain M855 bullet, which shows up as oblong holes in paper. The twist rate is often stamped on the barrel near the muzzle or listed in the rifle's specifications.

The 5.56 we stock

• MKE 5.56 SS109 62 grain FMJ battle packs: factory-new Turkish NATO-specification ammunition with brass cases, sold in sealed 450-round battle packs and 2,250-round cases.
• BVAC remanufactured Lake City M855 62 grain FMJ: loaded on once-fired Lake City brass, sold in 500-round packs. It is remanufactured, not factory new, and the product page says so.
• Federal American Eagle XM855 62 grain FMJ: factory-new M855-type ammunition in 150-round and 600-round packs.

All three use the 62 grain SS109/M855 bullet design with a steel penetrator, so they suit 1:7, 1:8 and most 1:9 barrels. If you need a lead-core 55 grain load, for example for a range that does not allow steel-core bullets, our .223 Remington line (PMC Bronze 55 grain FMJ-BT, brass case) runs in any 5.56 NATO chamber. The full lineup is in 5.56x45mm NATO.

Steel core is not steel case

People mix these up. M855 and SS109 have a steel penetrator inside the bullet, but the case is brass. Steel-case ammunition, common in 7.62x39, has a steel case. Many indoor ranges ban steel-core bullets because they can damage steel backstops and target hangers, and some ban steel-case ammunition too. A magnet test on the bullet tip tells you which you have. Outdoor ranges are usually more relaxed, but always check the posted rules. Our steel case vs brass case answer covers the case side.

Buying 5.56 by the case

Shipping is charged by weight, never free, so one larger pack usually ships more efficiently per round than several small ones. A 1,000-round case of 5.56 weighs roughly 27 to 30 pounds with packaging. Ammunition ships UPS Ground from our Phoenix warehouse. Check where we ship before you order. Phoenix-area shooters can call 480-623-4515 and pick up instead, Monday to Friday, 9am to 5pm. You must be 21 or older to order. Bring ID for pickup.

5.56 ammo questions

Can I shoot 5.56 NATO in a rifle marked .223 Remington?

Only if the maker says the rifle is rated for 5.56. 5.56 NATO runs at higher pressure than .223 Remington and a .223-only chamber has a shorter throat, so the combination can push pressure past what the rifle was built for. The reverse, .223 in a 5.56 chamber, is fine. Check the marking on your barrel. If it is worn or unclear, ask a gunsmith before you shoot it.

What is the difference between SS109 and M855?

They describe the same bullet design: a 62 grain full metal jacket with a steel penetrator over a lead core. SS109 is the original FN design name used in the NATO standard. M855 is the US military designation, and US-made M855 carries a green tip. Ballistically, the MKE SS109 and the M855 loads we stock are in the same class.

Is M855 green tip ammo legal to buy in Arizona?

Yes. M855 is sold to civilians across the United States, including Arizona. The limits you will usually meet are range rules, since many indoor ranges do not allow steel-core bullets. You must be 21 or older to order from us. See do you need ID to buy ammo.

How much 5.56 do I need for a carbine class?

Go by the round count on the course listing. Many one-day carbine courses ask for 300 to 600 rounds, and two-day courses often ask for 1,000 or more. Bring extra. Running out halfway through a drill costs you more than the leftover rounds do, and sealed ammo keeps for years.

How should I store a case of 5.56 in Phoenix?

Keep it indoors, in the sealed packaging or an ammo can, somewhere that stays near room temperature. Summer afternoons above 110 degrees Fahrenheit are routine in Phoenix, and a closed car or an uninsulated garage gets much hotter. Long heat exposure is not good for powder or primers. More in how long ammo lasts in storage.

More answers in our ammo FAQ, or compare calibers in 5.56 vs 7.62x39 and .300 Blackout.