There’s no question that heat and fouling are highly detrimental to moving parts in a firearm. The solution, however, does not necessarily require redesigning the whole gun. Fouling problems can be avoided quite easily with a marvelous little thing called lubrication.
“Keep her wet. That’s how you run an AR,” a hard-bitten range master once told me. “I don’t care what you squirt in there—BreakFree, WD-40, lime juice. It doesn’t matter. Soak her good.”
A good friend of mine, Sgt. Jason Davis of the Arcadia (Calif.) Police Department, has an M4 carbine with more than 2,500 rounds through it without cleaning. “I just keep it lubed,” he said. “I run it with a suppressor too, so it gets even dirtier. I’ve never had a malfunction, not one.”
Davis is not a glutton for punishing his gun. His no-cleaning test came about by chance.
“At first, I just didn’t get around to cleaning it, but after awhile, I realized I had a sort of torture test going without intending to. I wondered how long I could go without cleaning my M4, so I made a point of logging the rounds and just didn’t clean the gun. I lube it up before every session,” the lawman said.
I’ve never gone that far, but I’ve fired 1,500 rounds without cleaning, but I keep my bolt carrier wet. Reliability is not an issue with liberal lubrication.
Accordingly, it’s my opinion based on personal experience and a lot of anecdotal evidence that Eugene Stoner’s gas impingement system works as advertised. The piston system guns are, as the late Col. Jeff Cooper liked to say, “An ingenious solution to a nonexistent problem.”
Even if you take the argument of the piston system at face value—that it’s more reliable—you still have the law of unintended consequences to deal with. First, piston guns generate more felt recoil than impingement guns (although that’s not a huge detriment since we’re talking about a 5.56 mm here, a “poodle shooter” as Col. Cooper sniffed).
More importantly, however, a piston system alters the mechanics and timing of an AR in a manner that a growing number of shooters are claiming is harmful to the gun.
There are new systems being developed, tested and marketed now, but generally the problem is that a piston system is attempting to retroactively adapt a bolt carrier that was designed to function with direct impingement.
What we’re seeing are piston systems substituted for the gas tube of an impingement system by simply inserting a piston into the mechanism. The same buffer system is used to return the bolt carrier into battery, the same geometry of the bolt carrier is utilized and the same timing of the cycle rate is retained.
The only difference, really, is that a piston system gives the bolt carrier a mighty whack with a piston instead of blowing gas into it. The geometry is the same. The area of the bolt carrier that is being impacted by the piston is where the gas key would be on an impingement system. In fact, many of the piston systems simply replace the gas key on the bolt carrier with a flat-faced nubbin that is the anvil to the piston’s hammer.
This protrusion is attached to the bolt carrier well ahead (toward the muzzle) of its center of gravity. Going back to see-saw 101, we realize that if a force is applied well in front of a pivot, what happens? The rear tilts.
This see-saw effect is causing bolt carriers to tilt within the receiver, retarding their movement and imparting a non-linear force to the assembly. Stoner did not design the bolt carrier group to be hammered.
Perhaps the most “tacti-cool” of the piston systems is the HK 416 which came into the U.S. originally as a “military only” firearm in 2004 and then, much later, trickled out to law enforcement. The lure of forbidden fruit seemed to hype the public’s interest in the 416 and caused quite a bit of Internet chatter.
Then comes price. Ruger introduced a piston system AR—the SR15—that retails for over $2,000. I found an M4 from one of the more popular piston-gun makers listed on for $1,925. At the same time you can buy an excellent direct impingement AR for around $1,000.
At this fork in the road, I’m grabbing a bottle of BreakFree and taking the impingement path.
For more, check out Customizing an AR Rifle, AR-15 Tactical Accessories, The Specs of MilSpec and The MilSpec Definition.