Get a handle on your tactical rifle with <a href="" target="_blank">Gunsmithing the AR-15 — The Bench Manual</a>.
Get a handle on your tactical rifle with Gunsmithing the AR-15 — The Bench Manual.

Being the guy in the know, and with spies in all locations on the planet (or so some readers suppose), I get sent all sorts of interesting information. One of them concerns a recent incident with the U.S. Border Patrol. Apparently, someone from the higher echelons of management, sent armorers around to all the Border Patrol stations with orders to fully inspect all M4A1 carbines in use. In the course of inspecting, they apparently “deadlined” (that is, required removal from service) 65-70 percent of all rifles. This of course came as a surprise, and the powers-that-be had not planned to replace or repair that many rifles. So, the BP agents were reduced to one rifle per agent or less.

Now, in a city department, having one rifle for every other officer is not a problem. Backup is mere minutes away, and taking cover behind something substantial is an accepted practice when outgunned until the cavalry arrives.

However, Border Patrol agents are often miles and miles from anyone who might help. And they are in rifle country, with nothing solid to stay behind until help arrives. Not having rifles is a big problem. And there was a lot of consternation until the shortfall was corrected.

One of the tools the armorers used was a gauge I had never heard of called a Gauge, Gas Seal Hole, and is meant to be utilized at Depot-level maintenance. It measures the wear in the carrier bore hole, where the bolt tail seals. If the gauge goes all the way into the carrier, the carrier is worn out.

That such a tool exists does not surprise me. After all, the government has to have standards, measurements and inspection tools for everything.

What would surprise me is that any carrier, well, any properly-made carrier, would fail this gauge. Look, we have a hardened-steel part with wear surfaces that are hard-chrome plated. Rubbing against it is the tail of the bolt, but it isn’t really rubbing against it. The gas rings and the bolt body keep the bolt pretty well centered in the bore hole. The amount of actual rubbing has to be pretty minimal, and most of what is going on is carbon being created, ground off and pumped out of the gap. If there is gas leakage in that gap, I can see where the problem might be wear on the bolt from over-enthusiastic cleaning. But the carrier? I guess anything is possible.

Considering how grossly over-gassed even a properly gassed AR is, I’d bet that even if you had a carrier that failed this gauge, you could assemble it into a rifle and never notice the failure on the part of the carrier. Now, if you want to track down one of these gauges and use it, go ahead. But don’t think it is gaining you any advantage over your fellow shooters. And don’t think the gauge will be cheap, either.

If this was your original carrier, you’ve certainly gotten your money’s worth out of it if you have worn it out. Let’s just assume, for a ballpark figure, that the carrier in question has survived a decade of constant use. You’ve plugged four replacement barrels into the rifle, each with its own bolt. So, the original barrel and bolt, plus four more, at $75 each for the bolts and $150 each for the barrels. That’s $900 just in parts. Each of those bolt/barrel combos lasted you, what, 10,000 rounds? So that’s 50,000 rounds (don’t forget the original parts) and that, at the current price of ammo of roughly $300 per thousand, ran you $15,000. So, all told you have gotten the price of a new compact car of use out of that carrier. A new carrier to replace it costs you somewhere between $150 and $200.

Go ahead and splurge. Buy the replacement one with the super-high-tech plating on it to make it easier to clean. The extra $25-$50 is nothing in the scheme of things.

Editor’s Note: This article is an excerpt from Gunsmithing the AR-15 — The Bench Manual.


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  1. thank you Mr. Sweeney, pure logic as always. having an engineering back ground i can tell you have had the same. logic is the name of the game and that is why i do not understand the anti gun crowd. they only use emotion and it works with a lot of people. crazy world and crazy people. thanks again and have enjoyed your books that i have read immensely.