Advances in AR-15 Ammo

The .5.56 X 45mm/.223 Remington. This is the cartridge that started it all, when it comes to the AR 15. It is still the most popular, but its stablemates are ever increasing.

The .5.56 X 45mm/.223 Remington. This is the cartridge that started it all, when it comes to the AR 15. It is still the most popular, but its stablemates are ever increasing.

5.56X45mm NATO

It might seem odd to include the 5.56 NATO here, since it is the most popular AR-15 cartridge and the current military chambering, but the round has undergone considerable changes since its adoption. There are essentially two classes of this cartridge. The first and original class features light bullets like the 55-grain found in the M193 round. The second, epitomized by the Mk 262, Mod 0, and Mod 1 rounds developed by Black Hills, uses heavier bullets for long-range, precision shooting.

Built for the U.S. Navy’s Mk 12 SPR and now coveted by snipers and designated marksmen using similar rifles, the Mk 262’s 77-grain Sierra MatchKing projectile has a listed effective range of 600 yards, though it has certainly been put to use at longer ranges. It achieves velocities around 2,750 feet per second (fps) from 18-inch barrels and benefits from advanced propellants. Hornady loads a 75-grain hollowpoint boat-tail bullet in its .223 TAP line with similar specs.

Slower 1:7 twist rates are required to stabilize the heavier/longer bullets. Once they strike soft tissue, the bullets yaw and usually fragment to some degree, greatly increasing lethality over that of the more widely issued rounds like the M855 62-grain Penetrator or Green Tip. Serendipitously, the bigger bullets also perform quite well at close-quarters distances, when fired from short-barreled rifles like the Mk 18 (10.3-inch barrel) fielded by entry teams.

Shooters of all types have benefited from the military’s extensive efforts to improve on the 5.56mm NATO round, and now we have ammo options that extend the range and increase accuracy and lethality.

4 thoughts on “Advances in AR-15 Ammo

  1. capta45capta45

    “Slower 1:7 twist rates” – quite certain you meant either ‘slower velocity bullet’ or ‘faster 1:7 twist rates’. Obviously a 1:7 twist rate is faster than a 1:9 twist rate and will produce more rotation. Longer bullets generally need a faster twist rate to properly stabilize.

  2. retired75th

    There is a concerted ongoing effort to “sell” the 5.56. An effort to get the 5.56 to do what it is not cable of doing. If the platform, such as the AR and its variants was not so versatile, the AR in 5.56 would be a dying breed. It is the flexibility of the AR and not the 5.56 that sells the firearm. This is the bottom line. If you are engaging targets at 500 to 600 yes, are you seriously going to rely on 5.56? Of course not, so why push an inadequate round, except to make money. . There is a big difference between hitting the bulls eye on a paper target at 500 yds, and killing the enemy at 500 yds. If you are hooked on the AR, which is a good weapon, and want to engage real targets at extended range at least rebarrel the weapon. No firearm is the ideal for all missions and conditions, so base weapon selection on the mission, and not hype from folks with a financial angle. And one last thing, in what states is it legal to take big game with 5.56 as the author states?

    1. 454lvr

      Texas and Oklahoma are two that I know of that allow 223 to be used for deer. Oklahoma requires a 7 round or less magazine in the 223. If the ar is of the 308 variety you can used the 20 round magazine.

  3. Harold

    If you’re sticking to .223/5.56 mm, consider rounds that use Barnes TSX copper bullets. Black Hills makes loadings in both .223 and 5.56 mm, the latter to NATO and military specs, sealed, low flash powder and all that. They also sell to us their MK262 Mod 1 that you mention.