AR-15 rifles are highly customizable and whether you are building your own or purchasing one, there are many different choices you will need to make. One is which operating system to use: direct impingement vs gas piston. This is a hotly-debated topic among AR-15 owners. It can be helpful to know some of the basics of how these operating systems work and the differences between them before making a decision.
How a Direct Impingement Operating System Works
When a shooter pulls the trigger of a gun, the firing pin strikes the primer of the cartridge. This causes a controlled explosion which propels the bullet down the chamber and out of the gun. In a direct impingement operating system, the gas that this explosion generates is guided into a gas tube and is directed to the bolt carrier gas key. The gas then moves into the expansion chamber where it (as the name implies) expands and pushes the bolt carrier back. The gun then ejects the spent cartridge and a new round is loaded into the chamber.
Benefits of Direct Impingement
- Direct impingement guns are often better-suited to use with a suppressor.
- This operating system is more common for AR-15s and parts are typically standardized across different manufacturers. This makes direct impingement AR-15s easier to repair and maintain.
- Many shooters find direct impingement AR-15s to be more accurate. This is because the system limits the recoil more effectively, although this may not be noticeable in all cases.
Downsides of Direct Impingement
- Direct impingement operating systems heat up the bolt carrier group, which can be more likely to result in malfunctions. You will also need to let the bolt carrier cool down before removing it.
- Gas ports into the interior of the rifle, which creates more build-up in the gun and requires more frequent cleaning. This is one of the main reasons some gun owners prefer gas piston AR-15s.
How A Gas Piston Operating System Works
A gas piston system is fairly similar to direct impingement in that the force of the gas pushes the bolt carrier back to cycle a new round into the chamber. The difference is that a gas piston system works by forcing gas into a separate cylinder rather than using a gas tube. This cylinder contains a piston and the gas pushes this piston back, which then pushes the bolt carrier. This is in contrast to direct impingement where the bolt carrier is moved directly by the gas. The gas expels away from the shooter just above the gas block.
Benefits of Gas Piston
- Since gas does not port back into the gun, it stays cleaner for longer.
- Gas piston bolt carrier groups do not heat up as much as those in direct impingement systems.
Downsides of Gas Piston
- Gas piston AR-15s are heavier and have a stronger recoil. As a result, they can be slightly less accurate.
- Many gas piston operating systems are proprietary to the manufacturer, which makes it harder to find replacement parts if necessary.
- A piston-driven AR-15 will usually be more expensive than one that uses direct impingement.
Direct Impingement vs Gas Piston: Which is Better?
At the end of the day, direct impingement and gas piston operating systems both have their pros and cons. If you aren’t sure which you would prefer, you can try a few different types out at our shooting range. It’s also possible to switch out the upper receiver on an AR-15 so you can alternate between direct impingement and gas piston operating systems.