Understood...read that a GAS PISTON system really beats up the AR platform.
Operating Systems
The AR is a self-loading rifle that performs a basic set of functions without manual assistance from the operator. After the trigger is pressed, the gun must fire a cartridge, extract the fired case, eject it, pick up a fresh cartridge and transfer it from the magazine into the chamber, lock the breech and cock the hammer (or striker) to return the rifle to battery—a round in the chamber, ready to fire with another press of the trigger.
It’s really a straightforward mechanical operation. The best and brightest firearms designers have achieved it for the past 120 years with a variety of ingenious solutions.
Two of those solutions are the direct gas impingement system and the short stroke gas piston system. Eugene Stoner utilized the impingement system in the AR. It works by bleeding propellant gases through a port at the end of the barrel and channeling the gases back through a tube to directly strike, or impinge, a bolt carrier, thereby pushing it rearward to extract and eject the fired case and, as it’s propelled forward by a spring, to strip a fresh round and push it into the barrel’s chamber.
A short stroke gas piston system is what Mikhail Kalashnikov used on his AK-47. The piston system also relies on propellant gases that are bled through a small hole in the barrel, but instead of the gases traveling through a tube to impact a bolt carrier, the gases are contained in a cylinder in which there is a piston, like in a car. The gases push the piston, which in turn is connected by a rod to a bolt carrier that moves rearward to extract and eject the fired case and, moving forward from spring pressure, strip a fresh round from a magazine, chamber it and lock into battery.
What’s causing a fork in the AR road right now is that a number of manufacturers have decided to modify the Stoner design to operate with a piston system instead of an impingement system. The question before the house is: Do we need to fix the AR with a new operating system and, if so, do the new piston systems achieve that remedy?
An Answer In Search Of A Question
The sole claim to fame of a piston system is that it’s more reliable than an impingement system. The reason given is that hot, dirty gases are not spewed into the action of the rifle like the direct impingement system, fouling itself with heat and carbon, depositing black crud all over the bolt carrier. Instead, the gases are contained in a gas cylinder which is self-cleaning.
No one asserts that piston systems are more accurate or more durable, just that they’re more reliable because the bolt carrier is not caked with fouling and subjected to scalding heat.
Advocates of the piston system are quick to ask, “Why would you dump hot, dirty gases where your rifle feeds?”
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.”
Unintended Consequences
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.
https://www.americanrifleman.org/articles/2010/4/13/ar-operating-systems-gas-impingement-vs-piston/
