It is an old argument, however, we still field quite a few questions about which gas system is better. If you are new to the sporting rifle world, let me enlighten you on this little pickle that AR-and AK-heads fell into some time ago.
It started when people began to compare the AK-47 to the AR-15. This is no surprise since both rifles are common on opposite sides of the battlefield throughout the world. Most people know that the AK is famous for its reliability. However, accuracy has never been its strong suit. Still, wide proliferation, sales, and lore followed the AK as it spread across the globe and into the hands of every communist regime, rebel militia and foreign backwoods police force on the planet. In Vietnam, warfighters pitted the AK and M16—the military’s version of the AR—against one another. The M16, being a new design, fell victim to poor planning, incorrect powder and almost no training on the required care and feeding of this new rifle. The AK performed well in jungle conditions and subsequently earned the crown as king of all military carbines.
Eventually, the AK ended up in the hands of American civilians, who then had the opportunity to compare them closely to their AR-15s. In their standard issue configurations, the two famous rifles sported a detachable magazine, iron sights, and a semi-automatic action. However, this is where the similarities end. They represent two distinct approaches to carbine design. Mikhail Kalashnikov designed the Soviet rifle with loose tolerances, wooden stocks and handguards as well as simplified ergonomics. The weapon met the standards soviet leaders were looking for. They required a highly durable, inexpensive, select fire weapon they could put into the hands of a conscript with rudimentary training.
Unfortunately, the Soviet standard-issue AK was not a precision firearm. This is partially due to the loose tolerances, but the AK-47’s strongest advantage—its reliability—is also its most glaring weakness. The gas piston system (GP) keeps heat and fouling away from the chamber, thereby leaving the action to cycle unhindered by burning discharge from the powder. This gas piston system is what gave the AK-47 its famous rugged reliability. When that conscript soldier loaded a new magazine, he had 30 rounds to influence the battle—every time. However, this type of gas piston system causes more felt recoil, since there is a fair amount of inertia pushing back on the action during the case ejection. More felt recoil equals less accurate follow-up shots, especially when used in full-auto. Further, the barrel is not a free-float design, which also lowers accuracy. These two issues, combined with very rudimentary iron sights, work in concert to give the AK its reputation as a bit of a wild pitcher.
The original AR-15s use a direct gas impingement system (DI). This design moves gas from a fired cartridge directly to the bolt carrier, rather than using a piston above the barrel to push the bolt back. I should note, before anyone starts throwing things, that many ARs today are available with a piston gas system. However, you will pay a premium for these designs, and although they may indeed be extremely great products, it was not the original design for the AR platform.
The original DI design has a number of advantages, starting with accuracy. High-pressure gas acts directly upon the bolt and carrier thereby saving weight, lowering costs and reducing the mass of the operating parts. This reduction in mass increases the accuracy of follow up shots since less material is flying back and forth between shots. However, the main disadvantage of a DI system is that solids from the gas condensing on the bolt face and primary operating mechanism cause the breech of the firearm to foul more quickly. The combustion gases contain vaporized metals, carbon and impurities in a gaseous state until they contact cooler operating parts. The deposits increase friction on the moving parts leading to jams. Thorough and frequent cleaning is required to ensure reliability of this type of firearm.
What many fail to mention is the accuracy differences between the DI gas system of the AR, and the GP system of the AK inside 100 yards are in fact minimal. In G. L. M. Kjellgren’s publication, “The practical Range of Small Arms,” Kjellgren found the two rifles have about a 4-centimeter difference in group size at 100 yards with an average military shooter and iron sights. However, we should note that four centimeters could mean the difference in hitting or missing your target.
So, this still leaves us with the burning question, which gas system is better? For the modern AR-15 shopper, both DI and GP systems are available is a variety of configurations and from several manufacturers, so you’ll have to choose for yourself which one does a better job. To be sure, I wouldn’t want to get shot at by either.