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About 5.56x45mm NATO Ammunition

The 5.56x45mm NATO’s roots can be traced to the .223 Remington cartridge, a popular smallbore sporting cartridge. Initially, development for the cartridge began in the United States in 1957 alongside efforts to develop a smallbore, high-velocity firearm. This would eventually lead to the introduction of the AR-15 and subsequent M16 series of rifles.

The cartridge would go on to see use by American forces in the Vietnam War and subsequent conflicts. During the 1970s and 1980s, NATO expressed interest in a standardized, smallbore cartridge to replace the 7.62x51mm NATO round. This led to the cartridge’s adoption by NATO in the form of the SS109 cartridge.

After its adoption, the round has seen use with NATO members and allies such as the United Kingdom, Austria, France, and even Japan.

Types of 5.56x45mm NATO Loadings

• Full Metal Jacket (FMJ):Like the name suggests, these types of loadings feature projectiles which are adorned with metal jacketing. This jacket is generally made of copper and will cover the tip and sides of the projectile. Typically, the base of the projectile is left uncoated. These types of loadings are well-suited for range use and are some of the most common types of ammo one will encounter.
• Hollow Point Boat Tail (HPBT):HPBT loadings feature hollow point projectiles with boat tail style bases. These differ from traditional projectiles with flat bases and are well-suited to precision-oriented shooting. Like traditional hollow point loadings, these loadings are also designed to facilitate expansion on impact.
• Open Tip Match Boat Tail:These types of loadings will generally feature heavier projectiles and are well-suited to precision-oriented shooting. Unlike traditional projectiles, these offerings feature a streamlined boat-tail profile, facilitating better performance downrange. Material has been removed from these projectiles, hence the “Open-Tip Match” designation, helping achieve high velocities. While technically a hollow point, these loadings are designed for superior ballistic performance and not intended to function as standard hollow points.
• Tumble Upon Impact (TUI):These types of loadings from Fort Scott Munitions are designed to maximize the damage inflicted on vital organs upon impact. Like the name suggests, these defensive loadings are purpose-built to promote internal tumbling after impact. The result is a dynamic wound cavity and staggering internal damage, providing a user with potent fight-stopping capabilities.

Firearms that Use 5.56x45mm NATO Ammo

At this point in time, the market is full of firearms chambered in 5.56x45mm NATO. The most common types of firearms one will encounter in this caliber will be of the AR-15 variety. AR-15 rifles are incredibly common in the United States, a fact which makes the 5.56x45mm NATO cartridge one of the most common centerfire cartridges in the country.

Beyond AR-15s, a variety of other semi-automatic rifles can also be found in the caliber. Of course, manual action firearms such as bolt action rifles and lever action rifles are also available in the caliber.

5.56x45mm NATO Interchangeability

One of the most common examples of interchangeability on the market comes in the form of the relationship between the 5.56x45mm NATO and .223 Remington. The .223 Remington served as the basis for developing the 5.56x45mm NATO, a fact which explains their nearly identical dimensions as far as projectiles and casings go.

The biggest difference, however, is the fact that the 5.56x45mm NATO is a higher-pressure round than the .223 Remington. This means that 5.56x45mm NATO chambered firearms are able to accept .223 Remington ammunition. The use of 5.56x45mm NATO ammunition in a firearm chambered in .223 Remington is ill-advised due to the increased pressure of the cartridge.

While most firearms, regardless of caliber, are tested with overpressure loadings during the manufacturing process, a steady diet of ammunition of this type is not recommended. Luckily for shooters, the number of 5.56x45mm NATO chambered firearms outweighs the number of firearms exclusively chambered in .223 Remington.

This means that most of the time, shooters will be able to safely shoot either 5.56x45mm NATO or .223 Remington ammunition in their firearm without any worries.

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