AR-15 Chamber Selection, Part One

Accuracy, longevity, safety and function all hinge on chamber selection.

by Joe Carlos

If you want to start a good fight, get a barrel maker using button rifling in the same room as another manufacturer employing cut rifling. Perhaps the second bloodiest brew-ha would be to ask two armorers which is the best AR-15 chamber. If one of those gunsmiths happens to be a military builder and the other caters to civilians, the cuts and bruises will likely be worse. Since I have about a decade working for a big military shooting team and an equal amount of time catering to civilians, I figure I’ll be more than capable of ruffling a bunch of feathers in both camps.

This discussion will be limited to chambering for the original .223 Remington/5.56mm cartridge that most shooters are still using. The number of possible AR-15 chambers is nearly infinite. There are reamer companies out there that will custom build a chamber reamer to your specs leaving the possibilities almost as endless as the human imagination. Therefore, we will try to confine our discussion to the more common chambers in general use today.

The first questions to ask yourself or your customer are, “What is the finished gun going to be used for? What bullets will be fired in it?” Most folks will be using ammo set to magazine length which makes the chamber selection process much more limited. I cater to National Match Course Service Rifle competitors – the Camp Perry crowd. Most of them actually shoot two different bullets. Their match starts at 200 and 300 yards shooting magazine-length 75 or 77 grain bullets in standing and rapid fire strings and they finish all the way back to 600 yards where most switch to more wind resistant and heavier 80s or 90s. Since 600 yard shooting is a slow fire stage, shooters usually single feed their ammo and seat the bullets out well beyond fitting in a magazine. Chambers for these competitors are normally a compromise between what works best for the shorter ammo verses the long stuff and there is a fair amount of disagreement between gun builders on the specifics of those compromises. VLD bullets, bullets with thin jackets, military ammo, and brass and propellant preferences can also come into play in selecting a optimal chamber for any AR project. Specifics of the rifling will also need to be considered in some cases.

Read more in our July 2014 issue. Back issues are available.

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