AR Ammo Guide

This AR Ammo Guide goes over the most common types of AR chamberings and the ammunition most commonly used in these chamberings. Check out our other guides to learn more!

5.56 NATO

5.56 NATO is the most common type of AR chambering and is available in different grains and types, 62-grain M855 and 55-grain M193 being the two most common and mass-produced. The M855 (Green Tip) 62 Grain is a full metal jacket, boat-tail, and steel core with a muzzle velocity of 2700-3000 FPS (500 yards) and energy (muzzle) of 1,371 ft./lbs. (500 yards).

This round is best for 1:7/1:8 twist rate barrels, also known as fast twist rate. Although there have been reported instances of lack of penetration, these are over-exaggerated, as the round can penetrate 3 mm of steel at 600 meters. The M193 55 Grain is a full metal jacket, boat-tail with a muzzle velocity of 3,250 FPS and energy (muzzle) of 1,294 ft./lbs.

The 5.56 NATO round is best in a 1:10 twist rate (uncommon for common carbine barrel size) and can operate effectively in a 1:8 twist barrel. It is better against soft targets out to 100 yards.

The 5.56 NATO is a standard chambering and the ammo is easy to find and cheaper than other types of AR ammo. It is the most versatile of all rounds discussed and can shoot .223 from a barrel chambered in 5.56.

However, it is best in fast twist rate barrels; 1:8 is our preferred chambering for shooting M855 ammo, however, 1:7 is more than sufficient for this round. We do not suggest a 1:7 twist for M193, as it is a lighter round more suited for 1:9 twists.

.223 Remington

.223 Remington is the original AR-15 round circa 1964 and is also a popular bolt-action chambering/round. It comes in a wide range of grain sizes; 40-77 grains with a muzzle velocity of 3000-3700 FPS and energy (muzzle) of 1216-1333 ft./lbs. The biggest difference between .223 and 5.56 is the amount of pressure when fired. 55,000 PSI (.223), 58,000 PSI (5.56). 5.56 is packed with more powder and utilizes a heavier bullet, resulting in more pressure inside the rifle’s chamber.

It is important to note that you should not fire a 5.56 round out of a rifle chambered in .223.

The .223 Remington is best in slow-rate twist barrels – 1:9/1:10, this is due to the lighter/shorter bullet. The .223 Remington is more accurate when compared to 5.56 NATO, has higher quality/more options when choosing ammo in this caliber, and many match quality rounds are manufactured in this chambering. However, it is a more expensive round due to variance, and 5.56 cannot be fired from this barrel.

The .223 Wylde chambering is becoming more popular in AR-15 builds, and even from some manufacturers. This chambering allows for both .223 and 5.56 to be fired from this chamber while keeping the improved freebore concentricity, and inherent accuracy of the .223 Rem.

.300 AAC Blackout

The .300 AAC Blackout (often referred to as .300 BLK) is a popular round in short barrel rifles (SBRs) and AR pistols. It is a .300 caliber bullet in a  7.62 x 35mm casing and is known for its versatility and effectiveness at shorter distances. The .300 BLK cartridge has a bullet diameter of 7.8mm and can be found in heavier grain options, ranging from 110 to 220 grains.

Of these, supersonic options (110-180 grains) and subsonic options (190-220 grains) are the most common. The .300 BLK is best suited for shorter engagements, with a muzzle velocity of 2100 FPS and muzzle energy of 1000 ft./lbs at 100 yards.

However, it should be noted that bullet drop becomes more significant at longer distances and this round may not perform as well in medium to long-range engagements compared to the standard 5.56.

The .300 BLK has some distinct advantages over other rounds. Its higher energy and muzzle velocity at shorter distances make it well-suited for barrels shorter than 12.5 inches. Additionally, it can fit into 5.56/.223 chambered bolt carrier groups (BCGs), only requiring a barrel change to accommodate.

The .300 BLK is not well suited for long-distance engagements and has higher recoil. Additionally, it is a more expensive round and is not recommended to be used in barrels not specifically chambered for it.

It is important to note that firing 5.56/.223 cartridges out of a .300 BLK barrel could cause damage and should be avoided, and similarly, firing .300 BLK out of a 5.56/.223 barrel is very dangerous and can cause catastrophic malfunction and injury to the users.

.458 SOCOM

The .458 SOCOM is the lesser-known of all previously discussed rounds. It is derived from the .50 AE round, commonly fired from Desert Eagles. The bullet diameter is 0.458″ compared to 5.56’s 0.224″. It is a very powerful round, superior to all previously mentioned at shorter distances. The bullet weights range from 250 grains to 500 grains meaning it is a much heavier round than even the .300.

The .458 SOCOM has the highest effectiveness with ending threats at shorter distances, penetrates targets well, and is best for hunting large game and for home defense. However, it has short-range usage only, has the slowest velocity of all other AR rounds discussed, has lower magazine capacity due to the round’s overall size, cannot fit 5.56 BCG like previously discussed rounds, and is the most expensive by far on a per-round basis compared to 5.56/.223 and .300 AAC.

AR Ammo

Cartridge Specs

AR Ammo Guide Conclusion

Each of these rounds has its own set of pros and cons, and the best round for you will depend on your specific needs and preferences. It is important to remember that the 5.56 NATO and .223 Remington have different pressure levels and should not be fired from the wrong barrel. The .223 Wylde chambering allows for both .223 and 5.56 to be fired from this chamber, as does a rifle chambered in 5.56.

The .300 AAC Blackout is best suited for shorter distances, while the .458 SOCOM is best for short-range usage and hunting large game. It is always best to consult with a professional before making a decision on which round to use.

Be sure to read our other guides here!