Good barrels: the what and why

Guns Magazine, July, 2005 by Glen Zediker

There is essence to the AR-15 wahhoo component. I said the elemental trick was to "float a good barrel." Last time we got onto fore-end tubes, which is the "float" part, so now you need a "good barrel." and "'good" needs a good definition. Here's one: it's one that makes you happy with the accuracy of your AR-15. I can be a little more objective, but not any more honest. I expect my competition rifles to shoot groups less than 4" vertical at 600 yards. That's a 10-shot group fired prone with a scope. That makes me happy. Performance at that level takes a match-grade barrel, and that now takes another definition. This one, unfortunately, won't be objective.

In AR-15 Land you can't swing a dead cat anymore without hitting someone's "match barrel." The reason, or one reason, is that there are no standards, beyond those established by the maker hisself, that tell us what "match barrel" means. I say that a match barrel is one that wins matches. Cost is the best way to judge a barrel before purchase. However! The one thing I don't want to do here is tell anyone there's no chance of having an AR-15 shoot well unless he spends big for its barrel. That's wrong. I had a Colt HBAR barrel that shot as well as anything can. I've also seen HBARs that wouldn't hold minute of Bozo's nose. Same goes for the "match barrels" in common use on many pre-built AR-15s. Many shoot as well as one could ever hope for, but that's not good enough odds for a "shooter" (say it: "shootah"). We need brands that only very rarely don't shoot as well as one could hope for. Experienced competitive shooters become aware of this because we go through several barrels on the same rifle chassis, and we see a performance pattern develop. We want that pattern to be a flat line.

There's more to it. Distance shows difference. Let's take a decent barrel and a great barrel to the range. There will always be less notable difference in these barrels at 100 yards than at 200. More still at 300. Way more at 600. And night and day at 1,000. I've seen this too many times to respect it with a "maybe." I have squarely average barrels right now that shoot about as well as my best shooting barrels--at 100 yards. Full truth. One reason is that these barrels are all fairly fast twist rates and are firing bullets that aren't meant to shoot 100 yards. That matters, of course, and I would expect to see a more noticeable difference in short-range groups from a great barrel if both it and the average barrel were configured for 100-yard twists and bullets. Did I lose anybody else but me? What I meant to say is that distance always separates barrels. I also meant to say that a 1/8-minute difference in group size, for example at 100 yards isn't going to repulse most of us. The exception would be real Benchrest competition, but that's not a semi-automatic playground. I understand the security in accuracy "guarantees" given by many, and notice they are usually 3- or 5-shot 100-yard groups. I would like to see a 1/2 MOA guarantee for 20 rounds at 600 yards, but doubt I'll be functional flesh when that happens.

Go with stainless steel, especially for an AR-15. Stainless steel will not shoot one bit better than chromemoly, but will shoot better for a little longer. Expect another 10- to 15-percent longer sharp-edge accuracy from stainless. The reason is in how the steel "wears" as throat erosion progresses. Chromemoly tends to get rough (like sandpaper) whereas stainless steel tends to form cracks with still-smooth areas between them (like a dry lakebed). Interestingly, though, if we were going to shoot each barrel forever, the chromemoly would probably shoot the best past either's prime. When stainless groups open up, they tend to do so abruptly. Chromemoly group sizes cone outward more slowly.

How long a barrel lasts has to do with the load you shoot the most. If we plot out gas-pressure levels against bullet movement through the bore, we get a "pressure-time curve." Pressure levels are associated with respective levels of flame cutting. A steep P-T curve means more cutting, or at least it's more concentrated. It's clear the lighter bullets do less damage than heavier bullets, even though the lighter bullets mean burning more propellant. A steady diet of 77-grain bullets, for instance, will shorten barrel life compared to using mostly 55-grain bullets. Fortunately, .223 is one of the kindest rounds to barrel steel in competition use. I expect about 4,000 good rounds from a good barrel (about the same as .308 Winchester). In contrast, .243 Winchester provides about 1,200 rounds of X-ring accuracy.

RELATED ARTICLE: Twist.

The right twist (expressed in how many inches it takes for a bullet to make a full rotation) matters much in any AR-15 decision, but matters most when bigger bullets are in your plans. Bullet length, not weight, determines the twist rate needed for reliable stability. Longer bullets need a faster twist. For this reason, different profiles in same-weight .224 match bullets can mean different responses in different barrels. The most popular twist is 1:9. That's not enough. The best "all around" twist, I say, is 1:8. That will let you shoot anything up to and including a Sierra 80-grain MatchKing. It will also work fine with a Sierra 77-grain MatchKing, Hornady 75-grain Match, or similar heavier bullets designed to be loaded to magazine-box length. If you won't use anything currently made over 70 grains, then 1:9 is fine. If you won't use anything longer than a 55 grain, then 1:12 is not only fine, but dandy. Looking for an ultimate small group with one particular bullet does mean compromise with another, very different bullet. However, you can't get a longer bullet to shoot through a twist that's too slow. Get the twist that will stabilize the longest bullet you'll shoot and take what you get from that with any other. You scarcely, if ever, will notice your compromise.