A History of AR Cartridges

AR cartridges

The original caliber for the AR-15 wasn’t the.223/5.56, it was a slightly smaller cartridge. The .222 Special delivered the kind of performance that the designers wanted, which was basically a 50-grain bullet at under 3,000 feet per second.

The Army, trying to keep the AR away and keep the M14 in the running, kept moving the goalposts. Finally, they insisted that the bullet used had to penetrate a steel helmet at a distance farther than their own research had indicated soldiers fired on opponents.The special got stretched and boosted, until the 55-grain FMJ was at 3,100 fps.

And there it stood, until the mid-1980s, when the SS109 came about. That was intended for use against swarms of Soviet infantry in Western Europe. What, there never were swarms of Soviet infantry in Western Europe? Musta worked.

Seriously, the expectation was that the Soviets would roll West,and the NATO allies would be faced with Russian, East German, Polish and who knows who else mechanized infantry piling out of their BMDs, BMPs, and BTRs, lining up and assaulting the NATO positions. They expected to face lots of targets, and not only armed ones, but armored infantry. So, the push was for armor-piercing performance, leading to the SS109 and the laterM-855, with a 10-grain steel penetrator tip inside.

The new rifle also received a new barrel twist, one turn in seven inches, to fully stabilize the SS109 and the tracer as well. Only the tracer really needed the new twist, but the military approach was/is a “one size fits all” approach, so there it was. I had a talk with Mark Westrom, CEO of Armalite about that, and here marked that it would cost more to prove to the Army that a 1:9 twist was better than it would cost to re-barrel every rifle in inventory to 1:9.

Fast-forward to Somalia, the infamous “Blackhawk down” incident. There, good shooters (Rangers, Special Forces and Delta operators) spent a long time, and a lot of ammo, shooting at people who in many instances didn’t fall down when hit. To everyone’s surprise, small bore ammo designed to penetrate to a fare-thee-well failed to do more than create simple perforation wounds on unarmored opponents.

AR ammunitionSo the system stayed quiet until we were in another shooting war, and reports came back. This time, they came back too often, and too frequently, and over a long period of time, to be ignored. As a result, the now well-known Mk 262 load was developed.What it does is simple: it takes advantage of the too-fast twist of the M16A2 and M4, the 1:7 twist, and loads a 75- or 77-grain bulletin the case. The longer bullet is less stable than the shorter, 62-grain M855, and thus overturns on impact or soon after.

The next step was a refinement, the Mk 262 Mod 1, which included a cannelure in the bullet. The cannelure is a place to crimp the case neck into, but it also strategically weakens the bullet. When it begins to overturn on impact, it then breaks apart at the cannelure.

Stop wringing your hands. Lots of bullets overturn, tumble in the parlance, and lots of bullets have cannelures. And some have both, such as the old loading, the M-193, the 55-grain load from the Vietnam era.

The Mk 262 carries its speed better and offers longer-range performance. In fact, it offers too much long range performance, at least as far as hitting is concerned. You see, it puts the Army on the horns of a dilemma. The load is so accurate in some rifles that a skilled shooter can hit his target far beyond the effective ballistic “thump” of the bullet. Yes, a 77-grain bullet is gonna hurt, but when it has dropped to the performance of a .22 rimfire magnum, it gets tough to justify it.

What’s worse, not all (in fact, very few) of the soldiers who might get their hands on it can actually make use of its range. Yes, I’d rather poke a .224 hole through a bad guy at 700 yards,than let him walk off unscratched. The awful truth is, the Army doesn’t teach enough about marksmanship to let soldiers do that. The qualification course goes out to 300 meters.

There is no feedback, so if you nick the edge of the target you get scored the same as if you center-punched every one. Beyond 300 meters is a mystery, and many soldiers will be told to not shoot at the 300-meter targets, to save the rounds. That way, they can use the extras to make sure they get this close in. After all, with 20 targets coming up, and 20 rounds, you need only a dozen hits to pass. So, if the far targets are chancy, save your shots for the sure thing.

Which is a less than reassuring skill set to have, wedged behind a boulder in Afghanistan whilst being thrashed by a tripod-mounted PKM from 800 meters out.

No, the Army spends time teaching marksmanship skills to only a very few. They haven’t time, being too busy with a whole raft of mandated courses they have to teach first. But that doesn’t keep shooters from dreaming. The first dream was to stretch the existing round more. The longest-lasting and most-desired is to go back to the very beginning.

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