Last week I had a little chat with the guys at ArmaLite about my “issues” with their M-15 Service Rifle. For a brief recap, it had failure to feed issues all day at the first competition, and then continued to be a nuisance at the range. Pat, one of their repair technicians, had me do a quick test on the bolt carrier group and we quickly determined the nature of the problem. So what was this test?…
The real trick to the AR platform is in the bolt carrier’s gas rings (#7 in the diagram above). These are the little fiddly bits on the bolt that grip the inside of the bolt carrier and create a seal against which the hot gases from the direct impingement gas system press to cycle the action. If these gas rings don’t create a good enough seal, the action will not have enough power to completely cycle and will “short stroke,” failing to pick up the next round in the magazine. Sound familiar? It should, because that’s the exact problem we were having.
In a bolt carrier group (or BCG) that is within specifications the gas rings should apply enough pressure that, when placed upright standing on the bolt face, will support the weight of the bolt carrier while still allowing the bolt to move relatively freely.
Take a look at the lead picture. The bolt carrier group on the right is from my Pretty Princess SPR AR-15, and the one on the left is from the ArmaLite M-15. They should be the same height, and yet they’re not. This would seem to indicate that either the gas rings are worn out or the bolt carrier is poorly made (too large a hole).
ArmaLite was nice enough to send out four sets of gas rings for replacements, and extremely quickly too. Asked nicely on Friday, and they were in my mailbox Monday morning. They sent along two sets each of the individual rings as well as the spring-like single ring type, which took about 10 minutes each to remove the old and put on the new. Why do I say “each?” Because none of them worked.
Even with the new gas rings, the bolt failed to stay up (the Pretty Princess bolt, by the way, remained standing throughout this entire process). Even in different bolt carriers the bolt failed to stay up. In short, this bolt sucks.
There’s a general rule of thumb when you have as many AR bolts lying around as I do, and that rule is to always keep the same bolts with the same barrels. Swapping bolt carriers is cool, but the bolt (the actual part that touches the brass) should remain with the barrel it started with. The reason for this rule is that swapping around bolts can lead to headspace issues due to the different wear patterns on the guns. I fixed the problem with the M-15, but I had to break this rule to do it.
Both of my National Match rifles see very light use, especially compared to the other bullet tubes in my possession. They’re also pretty close in terms of total rounds downrange. Even though I could hear the comments coming a mile away (“what kind of shoddy, bad habit inducing blog do you run here!?”) I swapped the bolts, checked the headspace with my “go” and “no-go” gauges (it closed on “go” but didn’t on the “no-go”) and headed to the range. And this rifle functioned FLAWLESSLY.
30 rounds later and I’m convinced this rifle is fixed. Using the same ammunition I was planning on using for the match (Wilson Combat Match grade ammo, lovingly donated by Wilson Combat themselves) it had zero failures even when shooting offhand (the position with the least buttstock support). The next competition on the schedule is this weekend, and I’ll be returning to Bridgeville Deleware for an 800 point Across the Course competition. This is the exact same place where I had the issues last time, we’ll see if history repeats itself.
Solution: New bolt and bolt carrier.