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5.56 NATO ammunition: A helpful guide

5.56x45mm NATO ammunition is a type of rifle ammunition developed by the US military and in part with their NATO allies. M193 and M855 are the two most common 5.56 NATO rounds. 5.56 NATO has been standard issue rifle ammunition for the U.S. Military since the 1960’s. It is also used by all of our NATO allies.

Development of the 5.56x45mm

After WWII, studies conducted by the military had indicated that the average engagement distance for US troops was less than 200 yards.

The military set out to develop a cartridge for a new rifle that would feature a detachable magazine. Ultimately they settled on the 7.62×51 NATO and proceeded to force it upon NATO allies. Many of these allies, such as the British, had wanted to go with a smaller cartridge than that.

While the AR-10 had been late to the military trials for a new service rifle, it left an impression. A faction of the US military still wanted to explore the idea of a smaller caliber rifle than the M14. They would convince Eugene Stoner to scale down the AR-10 to a smaller, high velocity cartridge.

Initially, the .222 Remington cartridge was chosen, but it was determined that the cartridge was not hot enough. They decided to lengthen the case and create a brand new cartridge which would be known as .223 Remington on the commercial side. The 5.56x45mm NATO was born.

The USAF quickly adopted the M16 in this new cartridge. During this time the Vietnam war was ramping up and there were production issues with the M14. As a stop gap measure, military brass ordered more M16’s and the M16 and its 5.56x45mm cartridge took off.

What is the difference between 5.56 and .223?

The outer dimensions of these two calibers are exactly the same. However, the chambers for the two calibers are different. 5.56 chambered weapons have more headspace and a longer throat than .223 Remington. This is because 5.56 is loaded hotter and generates more pressure than .223 Remington.

SAAMI warns against using 5.56 in .223 Remington chambered firearms. This is particularly important with older firearms. However, you shouldn’t have a problem shooting SAAMI spec .223 in a 5.56 chambered firearm.

.223 Wylde chambers are made to be able to shoot both as well.

As a general rule, a .223 Remington chamber should offer better accuracy. If pin point accuracy is not your top priority and you want to shoot a wider range of ammo, you should consider a 5.56 or .223 Wylde chamber.

Some manufacturers mark their barrels or firearms as being “.223” when they actually are chambered for 5.56. if you have any questions you should contact the manufacturer for clarification.

What types of 5.56 NATO are being used in the US military?

There are many different types of 5.56 in use with the US military. They include:

  • M193: A 55 grain lead-core FMJ bullet. It has a copper jacket and is non-magnetic. M193 was adopted by the US military in 1964 and is still in use today.
  • M196: A 55 grain tracer round. It is identical to M193, except for the addition of a trace element in the bullet. It has a red tip so that it is differentiated from M193.
  • M855: A 62 grain lead/steel-core hybrid FMJ bullet with a steel penetrator tip and a copper jacket. It is magnetic. M855 was adopted by the US military in 1983 though the SS109 bullet which it utilizes was developed by NATO allies.
  • M856: A 62 grain tracer round. It is identical to M855, except for the addition of a trace element in the bullet. It has an orange tip so that it is differentiated from M855.
  • Mk262 Mod 0/ Mk262 Mod: A 77 grain Open Tip Match (OTM) bullet. It is a lead-core bullet with a copper jacket and a boat-tail design. The tip is open to improve accuracy.
  • M995: A 62 grain armor piercing (AP) round with a tungsten carbide penetrator. It has a black painted tip.
  • M855A1: A 62 grain lead-free copper-core bullet made for better performance in shorter barrels.
  • Mk318: A 62 grain lead/copper hybrid construction bullet with OTM for better accuracy and barrier penetration.

Many of these rounds are being issued on a limited basis.

50/200 yard zero

One of the most popular 5.56x45mm zero’s is the 50/200 yard zero. This means that your rifle will be sighted in such that your bullet will impact dead on at 50 yards, and have a similar point of impact at 200 yards. At 100 yards, the point of impact will be about 1-2″ high. At 300 yards, you’re point of impact will be about 5-6″ low, and at 400 yards, it is about 12″ low.

The advantage of zeroing at this range is that you have a fairly similar point of impact at ranges under 200 yards. Even out to 400 yards, you might be able to make COM (center of mass) hits without much compensation for elevation.


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