In Part I, I wrote about barrel essentials, mostly manufacturing methods and materials. This time I want to cover other considerations in choosing a barrel for your AR-15, including contours, length, life expectancy, crowns, cryo treatments and chambering choices.
The first is contouring, and that means the barrel diameter at different points along the tube. If it’s a replacement barrel for an issue-style A2, the dimensions are pretty well set for us to fit the front sight housing, and the only optional point is the area under the handguard tube. Most competitive NRA High Power Rifle Service Rifle shooters want the rifle to be just as heavy as it can be, and that’s because the short barrel doesn’t provide the extended “leverage” to hang still when held from the standing position. For example, my Service Rifle weighs 13 pounds, with lead added in.
Otherwise, and for different applications, especially if you’re using a stress-relieved barrel, it’s not necessary to go too heavy (thick). A very heavy barrel will not make your rifle shoot any better. Promise! Well, within reason. By that I mean maintaining 0.750- to 0.800-inch diameter will group just as well as anything that’s a full inch. A lot of the “varmint”-style barrels or the bull barrels (parallel all the way) are just too big. In my way of thinking, there’s no reason to carry a 12-pound rig around when a 9-pound rifle shoots just as well.
In choosing a carbine barrel style, keep in mind the hangers-on you might want to add. It’s popular to increase the barrel diameter under the hanguard to increase rifle weight. The addition does, indeed, make the short guns hang better. But, if you then add a few Picatinny-mounted utilities, your carbine can get heavy. I won’t make a recommendation, just this suggestion: total up the appliance weights before you decide on the barrel contour, and chances are you’ll keep it around 0.800 inch diameter.
Barrel length is another question, when it’s an option. The .223 Remington round doesn’t benefit as much from longer and longer barrels as will a higher-volume cartridge case. There’s about 80 to 100 fps gain from the issue 20-inch compared to a 24. That’s a gain, no doubt, but there’s hardly any difference in anything longer. Unless necessary changes have been calculated and incorporated, a longer barrel will have a strong influence on cycling. I’ll talk about the operating system in a future piece, but the essence is that an issue-spec gas port size and location, in a longer barrel, will increase gas port pressure. Increased port pressure makes for more vicious cycling. The reason is simply because there’s more gas contained within the barrel for a longer time. If you are a handloader, you’re likely to get shorter life from cases because the increased port pressure will result in quicker unlocking. It can create other issues that have to be worked around, and we’ll get to those soon enough.
How long an AR-15 barrel lasts has to do with the load you shoot the most of. The life of a barrel is in the throat; there’s insignificant wear on down the length of the tube. If we plot out propellant gas pressure levels against the progression of bullet movement through the bore, we get a “pressure-time curve.” Pressure levels are associated with respective levels of flame cutting in the chamber throat area.
A steep p-t curve (slower moving bullet) means more cutting, or at least it’s more concentrated. It’s clear that lighter bullets will do less damage than heavier bullets, even though the lighter bullet loads contain more propellant. A steady diet of 77-grain bullets, for instance, will shorten barrel life compared to using mostly 55-grain bullets.
Fortunately, .223 Remington is one of the kindest to barrel steel of rounds in common use. I expect about 5,000 good rounds from a good barrel (about the same as .308 Winchester), and that is using primarily 77-grain bullets.
I’d add another 2,000 rounds to a barrel fed a varmint-type bullet diet (52 to 60 grains). In contrast, something like .243 Winchester provides about 1200 rounds of X-ring accuracy. There’s also little doubt that hold quality factors heavily. A High Master class competitor is going to think his barrel has gone bad sooner than a Marksman will. If you’re shooting targets at 100 to 150 yards, you will likely be able to shoot 12,000 or more rounds and still be well within a quarter-size group.
Cures for Lack of Accuracy
Are there any cures for a barrel that’s not grouping up to your standards, or a way to improve a factory barrel? Well, maybe, but not likely. The cause for the poor performance determines that answer, and sometimes that’s hard to know until any tricks have been tried.
One is a muzzle recrown. That’s not terribly expensive and, you bet, bad crowns are prevalent on factory barrels and fixing one can be like a miracle.
Next is trying some sort of bullet-lapping product and procedure, such as David Tubb’s FinalFinish. I have seen that work wonders, especially on a factory barrel. It polishes the bore, and also the leade area.
I would not advise a cryogenic (deep freezing) treatment in hopes of seeing much influence. Those can sometimes make what’s there a little better, but it won’t fix anything that’s wrong.
I plan to do a complete piece on chambers and chambering, but for now I’ll recommend a NATO-spec chamber (5.56x45mm). The commercial .223 Remington chamber has too short a throat for use with mil-spec ammo (this is sometimes called a “Match” or “SAAMI Minimum” chamber in barrel ads). Just because it says “Match” doesn’t mean it’s good, it’s just short. NATO takes anything.
Of course, if you’re a competitive shooter, there are a few more options, but we tend to use something that’s between those two, leaning closer to NATO. The only group I could suggest a .223 Remington chamber to are varmint hunters who will NEVER attempt to fire surplus or mil-spec cartridges, but instead a steady diet of bullets under 62-grain weights loaded to commercial specs.
What do you do to improve barrel performance? Share with us in the comment section.