AR15s can have problems “over-functioning.” There are two essential ways to make your AR15 behave better! Here’s the first…
Glen Zediker
Right. I know this column is about handloading and reloading, so why am I spending space talking about gas system function? Well, it’s ammunition-related, or, at the least it is influenced by ammunition, and therefore also influences ammunition choices.
First, an AR15 gas system “over-functions” when it fills up too quickly and with too much burned propellant gas. The AR15 uses a “direct impingement” gas system, sometimes called an impulse system, and that means there’s a port hole in the barrel that lets gas out and through a gas tube, and this gas goes directly into the bolt carrier key and sends the whole works backwards. There’s no piston (although piston systems exist that can be fitted to these firearms) or other regulating device beyond gas port hole location and size.
The effect or upshot of over-function is overly quick bolt unlocking. The symptoms include extraction problems, damaged case rims (related), overly-blown cartridge case shoulders, excessive case head expansion, and, generally, accelerated wear on the action hisseff. As with many things, the severity of the excess function likewise increases excess in its manifestations.
What happens is that the case is swelled up under pressure inside the chamber, as it should be, but then it’s still swelled up when the bolt opens and the extractor takes a yank on the case rim to get it out of the chamber.
With respect to handloading ammunition, keeping the bolt in battery a tick longer makes a world of difference in spent case condition. The case has a tick more time to return to closer to normal dimensions and shrink away from the chamber walls. And time is, again, what this is really about. The case will be less stressed and dimensionally nearer original specs, and that means there’s “less” sizing done for next use, in effect. Case life improves and also does longer-term quality for reuse.
So. If we can delay bolt unlocking we’re seriously on to something. The simplest way to slow something down is make it heavier. Heavier things don’t accelerate as fast, they have a greater “moment of inertia,” less resistant to initial movement. Increasing bolt carrier mass is very effective. Keep in mind that what unlocks the bolt isn’t bolt movement, it’s bolt carrier movement. The bolt movement is a natural oucome to rearward travel of the carrier. Minor point but, well, there it is. I run “M-16 style” bolt carriers in all my AR15s. That’s a carrier with a full round section at the end rather than the notched out profile of the standard semi-auto carrier. And, no, an M-16 carrier won’t make a gun full-auto, and, as a matter of fact, carriers with the full-round profile are routinely encountered as “match” bolt carriers. Heavier is better!
Anything contacting the bolt carrier can increase in weight also and be effective. That effectively increases the load against the bolt carrier, and that requires more time to overcome and create movement. The buffer, for instance. I always run heavy buffers in my short guns, and also my hot-rod rifles for Across The Course use. The carbine-length stocks use a shorter spring and also a shorter buffer, and that means a lighter buffer.
More about the spring’s role in all this next time, along with other more major modifications that will downright tame an AR15. And I’ll also run down a step-by-step on ensuring reliable function in a slowed-down AR15.
The preceding was adapted from Glen’s newest book, Top-Grade Ammo, available here at Midsouth. For more information on this book, and others, plus articles and information for download, visit ZedikerPublishing.com
