Direct impingement or gas piston for your AR-15?
If the AR-15 rifle isn’t currently the top selling rifle in the country, it is right there near the top.
Recently, retailers have had trouble keeping AR-platform rifles in stock. There are several reasons for the AR-type rifle’s popularity. They are lightweight, reasonably powerful, accurate and highly customizable due to an industry of accessories that have built up around the AR-style rifles. They also feature a detachable magazine and semi-automatic self-loaders, and their recoil is minimal.
One dilemma that buyers have to deal with is determining which operating system they want in their AR rifle. The choice is between the traditional direct impingement system originally designed by Eugene Stoner, or the gas piston system that was introduced in modern rifles by Mikhail Kalashnikov in the AK-47 rifle.
Once fired, the direct impingement system bleeds propellant gases through a small hole in the barrel, which is channeled through a tube where it can directly contact or impinge the bolt carrier mechanism. At this point, the gas pushes the bolt carrier to the rear of the rifle, extracting and ejecting the spent case.
The bolt carrier is then pushed forward by a spring and strips a new cartridge from the magazine, which it pushed into the chamber of the rifle and locks behind the cartridge. Another pull of the trigger starts the whole process again.
Contrary to the claims of some, the direct impingement system is very reliable and jams are a rare occurrence. Many who have tested direct impingement have fired thousands of rounds through the AR-15 before cleaning with no malfunctions or jamming problems.
My own experience with my first AR-15 has been the same, except I do clean my rifle after each outing and range session. My grandchildren, though, have taken turns shooting it at the range almost all day long and have experienced no malfunctions.
The bolt carrier of a rifle using the direct impingement system does get really hot after extended shooting, and a cool down period is necessary before trying to remove the bolt carrier from the rifle by hand.
The firing process with a rifle containing a gas piston starts with the propellant gases being bled from a small hole in the barrel, as well. However, instead of being forced into a small tube, the gases are contained in a cylinder containing a piston.
The gases move the piston, which in turn pushes the bolt carrier to the rear of the rifle, extracting and ejecting the case. A spring then moves the bolt carrier forward, stripping a new cartridge from the magazine, pushing it into the chamber of the rifle and locking the bolt carrier behind the cartridge. The next pull on the trigger starts the whole process again.
The claims that gas piston operation is mechanically unsound can’t be verified, as far as I know. Just ask anyone who owns the semi-automatic version of the AK-47, or just ask any Vietnam veteran if they ever heard of an AK malfunctioning or jamming.
The question of which operation is superior is a matter of opinion, and there are many opinionated owners of both operation systems.
The direct impingement system does produce hot bolt carriers after extended firing, and the breech bolt and its carrier get dirty and require regular cleaning and maintenance. However, the AR-15 is accurate, reliable and inexpensive. Plus, parts are easily obtained, generally to Mil Spec standard.
The gas piston operation now being offered in several manufacturers’ AR-platform rifles produce a cleaner, cooler operation that allows removal of the bolt carrier by hand immediately after extended shooting. The gas piston system does produce a snappier recoil after each shot, making it a little slower to get back on target for subsequent shots.
The trade-off is that the gas piston parts are not interchangeable between manufacturers due to there being no set standard.
So, choose your operational system according to your personal preferences and don’t be too hard on those who don’t share your specific preferences. Both operating systems are reasonably simple, phenomenally reliable and have more positives than negatives going for them.
Smokey Merkley was raised in Idaho and has been hunting since he was 10 years old. He was a member of the faculty of Texas A&M University for 25 years. There he taught orienteering, marksmanship, self-defense, fencing, scuba diving and boxing. He was among the first DPS-certified Texas Concealed Handgun Instructors. He can be contacted at email@example.com.