Big bullets: slower now, faster later

Guns Magazine, Dec, 2007 by Glen Zediker

Here's a good question. Are we, A) trying to make the AR-15 into something it's not and never can be, or are we, B) making it better, making it all it can be? I say "B." Sometimes it seems like "A." Keep reading. I'm speaking of extending the range of .223 Remington, which has always been the overriding limitation of its rifle.

The idea of running longer, heavier bullets through an AR-15 is by no means new. As a matter of fact, it predates the rifle hisself. Back in the early 1950s our Armed Forces got an idea a smaller caliber projectile would be the hot ticket to the field hospital for enemy troops. That was, of course, when we were using 30-caliber rounds in battle rifles. The "SALVO" project developed a 68-grain 224-caliber bullet, which was a scaled-down 30 caliber. Photos are nearby. These bullets were produced by the then new and California-based Sierra Bullets. The cartridge used for these tests was similar, ballistically, to .223 Remington (but wasn't .223 Remington).

About 10 years later, Mike Walker, who worked for Remington, experimented with his take on a heavy .22--a 90-grain. He also did up some 105-grain .243s. Nothing then came of either, beyond notebooks full of notes. Essentially, there were no dries of the day suited to work well with such a heavy projectile and, therefore, little commercial interest in the concept. Remember, before AR-15s stormed NRA High Power Rifle in the mid-1990s, primary use of centerfire .22s was near-about exclusively relegated to varmint hunting or Benchrest for sport and 55-grain magazine-fed rounds for battle.

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These bigger bullets all came back. The reasons are many, but it's really the point to the combination of heavy bullets and small-caliber rifles. The combination makes it work. It's not one thing. Well, the one thing it ultimately is, is the need to make an AR-15 competitive at distance, which for me and mine is 600 yards.

New World

Sierra opened up a whole new world (well, at least another 100 yards of it) to AR-15 shooters with the introduction of its 69-grain MatchKing bullet in 1984. This was, as best as my research could show, the first commercially-available "long range" .22 bullet. Jimmy Knox of JLK Bullets did the big do, though, in my estimation, when he had Bill Davis design an 80-grain VLD (very low drag) .224 in 1990.

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The Sierra 69 is an outstanding bullet and perforates exceedingly well, but clutches its side and collapses when it has to run past 300 yards. The 80 VLD can, will and did, beat the then dominant 168-grain .308 bullet in use in Lake City Match M852 at 600 yards. That's what (whether real or replicated) we, or most of us shot in our competition-use M1As. Sierra followed very soon after with its 80-grain MatchKing, and it's been the one to beat, and therefore to use, ever since.

None of that really matters, but, well, there it was. I think there's some sort of gunwriter's creed to include a historical perspective on cartridges and such. Check. What really matters, of course, is getting the daggone things to shoot, if you want to shoot them.

You want to shoot them if you have to. Otherwise, the round structure is better, and performance surer, at least simpler, sticking with anything under 70 grains. If you are going to shoot heavy bullets, then barrel specifications have to support the notion. Namely, twist rate and chamber length. Of these, the rate of twist (one turn in how many inches) in the rifling matters most. Long bullets need a lot of rotation to stabilize. The minimum for an 80-grain bullet is 1-8", better is 1-7". If you have a 1-9" twist barrel, you'll see something out of one of the 75-grain bullets, but maybe not even all of them.

The same thing happens with .223 Remington as it does for any cartridge when the bullets get longer and heavier than original blueprints called for. Lower velocity. And if the round has to fit an overall length restriction (all do at least to some degree), less propellant capacity. Likewise, heavier and heavier bullets generally perform better and better when fueled with slower and slower burning propellants. Lower case capacity, more propellant ... something else has to change.

The chamber throat is, next to rifling twist rate, the most important determiner of forecasted success, or so I say. Most factory-chambered AR-15s, at least those with "match" barrels, are too short in the distance between cartridge end and rifling start.

To make long bullets work, and it's really length more than weight, the bullets have to be scooted out about as far as prudence allows. Prudence says keep the major diameter of the bullet body within at least 2/3 of the case neck. The little sawed-off case neck. Prudence bites. The chambers in my competition rifles are very long, by industry-reamed standards.

Chamber Matters

High Power folks usually talk about chamber lengths based on the loaded-round length putting a Sierra 80 just touching the lands when the round is chambered. A true SAAMI-minimum chamber will normally be around 2.350" based on that means of measurement. Those I use are 2.550". That's a huge difference. Of course, that means the bullets I shoot from the magazines are jumping a great deal to get into the rifling, but the tradeoff for better long-range performance from 80- and 90-grain bullets has to be the preferred compromise.