Got Gas...?

by Ben Small

Lately, I've been seeing articles, ads and television programs on the Sportsman Channel (DirecTV) and others about new gas systems for AR style rifles, both the AR-15 and AR-10, and of course, their military counterparts, the M-16, the M4 and the M14.

While AR-style rifles are considered much more accurate than the AK rifles most insurgents and third world bad guys use, they're also more fallible, i.e. they fail a lot. ARs are notorious for two aspects: They must be clean and they must be wet. If these two criteria aren't met, the guns may not fire, especially when it's hot outside or the rifle's fired a number of rounds between cleanings.

If a rifle doesn't fire, the shooter may die.

Contrast this with the AK-47, a simplistic design that will fire every time, even if the rifle's never been cleaned. The AK-47's design is so simple -- intended to be so -- that a kid can assemble and operate one.

Why the difference? Two reasons, really. ARs have tight tolerances and a direct gas impingement system, whereas the AKs have loose tolerances and are gas-piston driven.

Big deal? You betcha.

The problem with ARs is fouling. There's a small hole in the barrel which directs some of the gases from a fired round all the way back through the rifle's upper, forcing the bolt back into battery so it's ready for the next shot. But when the gases come back to the receiver and bolt, they bring unburned powder and other contaminants, thereby fouling the bolt. Over time, due to the tight tolerances of the ARs, the gun will cease to operate. Sprinkling some gun oil into the bolt and receiver area will free it up for more rounds, but the receiver and bolt chamber will be filthy, and each round fired will make them more so. Eventually, the gun will malfunction again unless cleaned and re-oiled, a messy proposition.

In the AK, however, a hole in the barrel directs the gases and contaminants to a spring loaded piston, which drives the bolt back. No contaminants reach the receiver or the bolt, and because of that and the loose tolerances, the bolt doesn't need oil. Some AKs, fired for years, may never have been cleaned and oiled.

Top end manufacturers have caught on to this AR issue, and now they're starting to produce ARs that are gas-piston driven, much like the AKs. FNH is now making ARs with gas-piston uppers, as is Les Baer. Same with Sig Sauer, with its new 556 line of rifles.

When Sig first came out with its 556 line -- a version of its war-proven 55X rifles -- many internet gun bullies corrected those who called the 556 an AR-style rifle, saying the 556 was more of an AK design than an AR design. Because of the gas-piston system. But now other AR manufacturers are releasing gas-piston driven AR rifles, so the nomenclature bullies are being driven back into their internet holes.

The beauty of an AR with a gas-piston system should be self-evident: The gun is accurate and clean. Tolerances remain tight, but contaminants can't reach the receiver and bolt. Less chance of a malfunction. And the Sig has an added benefit; you can adjust the gas system. Say, for instance, you've shot many mags through your rifle and due to heat and maybe some burned oil, and the rifle is acting sluggish, maybe not slipping fully into battery. Just turn the nozzle at the end of the upper and increase the gas level. Position one to position two. Problem solved. Shoot three hundred more bad guys.

So... why tell you all this? Because for a novelist, the devil is in the details. And some of these details may just give you an important plot point.

For a good discussion of this important and developing design change in military and commercial "black" rifles, see Direct Gas Impingement vs. Gas Piston Driven