Is Direct Impingement Better?

If you’ve ever spoken to any owner of an AR 15, you’ll probably have noticed that we have a lot of opinions about our firearms. We can happily debate for hours about the benefits and detriments to a longer or shorter barrel length, the weight versus versatility of different handguard rail systems, and so on. The AR 15 was designed to be easily customizable, which means that every AR owner can create a firearm that meets their personal tastes and specifications. Of course, with so many options for alterations and changes, there are just as many—if not more—opinions about which options are the best. As custom AR parts manufacturers, one of the questions we hear most often is about the gas system that powers the action. Is direct impingement better or worse than a gas piston system for powering the bolt carrier group? Here are a few things to consider:


Why It Matters

First and foremost, in order to really get into this debate, it’s important to know why the question of direct impingement versus gas piston even matters. As any AR owner should be able to tell you, both direct impingement and gas piston are systems used to fire a round, eject the spent cartridge, and cycle through to chamber a new round. Both systems use the force of the gas created from firing to force the bolt carrier group back to go through the ejection and reloading action in one smooth step. For more information about the carrier group, see our previous blog post here. Since both systems accomplish the same thing, logic says there shouldn’t necessarily be a debate on the topic. And yet, the debate still comes up time and again.


Direct Impingement

The only big difference between direct impingement and gas piston is where the gas goes after helping expel the bullet through the barrel. In a direct impingement gas system, the gas created from firing gets pushed along the barrel with the bullet until it hits the gas block. At that point, the bullet will continue out the barrel, but the gas is forced up into the gas tube and directed back along the length of the barrel and into the gas key, at which point the gas forces the carrier group back to eject the spent casing and load the next round.


Gas Piston

The difference between the two systems seems like a trivial one, but it can have a noticeable impact over time. With the direct impingement, it’s the force of the gas from firing that cycles the action. A gas piston cycles the action in the same manner, but with a key difference: the gas never cycles back to the carrier group. Instead, when a shot is fired, the gas forces the bullet down the barrel and reaches the gas block, but instead of traveling along the gas tube and back into the chamber, the gas stops just above the gas block, hits a solid piston, and expels out at that point (away from the user). Because the gas still goes up and out of the barrel with the same amount of force, it still has the power to cycle the bolt carrier group just as effectively.

The Difference

When it comes to firing, the difference in sensation between direct impingement and gas piston is minimal. Someone of a smaller stature may experience a bit more kickback from the gas piston system, but otherwise the difference when firing direct impingement and gas piston is negligible—particularly when you have an adjustable carrier group to control the level of gas suppression. The primary difference, and the reason so many AR 15 owners rave about switching over to the gas piston system, is the level of cleanliness. In the direct impingement system, it’s the dirty gas from firing that gets pushed back into the chamber. If you aren’t diligent about cleaning your firearm, that gunk can build up and cause misfire or jamming issues. Because a gas piston system uses the force and expels the gas outward, none of that debris filled gas will hit the chamber. Of course, if you clean your AR regularly, a direct impingement system isn’t any more or less effective.


Experience the difference and make your mind up on this debate. Shop custom machined carrier group options and more online from Bootleg, Inc.!

1 thought on “Is Direct Impingement Better?”

  1. Normal cleaning of a direct impingement firearm doesn’t remove the crud-laden debris deposited in the tube carrying gases back to the carrier. Impossible to clear it in the field. Major Senate investigation found G.I.s were found with cleaning rods still in the tube, when they were killed. Defense contractor had used a ball powder, that didn’t burn as cleanly as the IMR powder in the contract! Quick fixes included a chromed chamber and puch bar to force a round home. Not worth my life to see, if the problem was solved. Debate over.

    A piston block system is easier to clean for the average owner.

    Helicopter Crewchief 68′-69′
    A/2/17 Cavalry, 101st ABN

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