Since I’ve had the opportunity through testing and reviewing guns for various firearms periodicals to test both gas impingement and piston-driven ARs, I’ve realized there are a number of advantages and disadvantages to both varieties of ARs. What I’ve come down to are six major differences between piston-driven and gas impingement AR rifles.
1. On average, the piston-driven rifles I’ve fired have been less accurate. I’m not saying they are inaccurate rifles, but the most accurate ARs I’ve tested over the years have been those that work with the gas impingement firing system.
2. Piston-driven guns are quite a bit cleaner after firing. If you fire a 30-round mag through a piston-driven AR, it will pretty much look just as clean afterwards as before you even fired it.
3. Between gas impingement and piston-driven guns in the heat test, the piston-driven guns run much cooler. You’d have to shoot at least a hundred rounds through both types of guns to really feel a difference, but there is a difference.
4. If you want to run a suppressor on your AR, you will likely find gas impingement guns to be more suppressor-friendly than piston-driven. This is especially true on gas impingement guns that have an adjustable gas block to regulate how much gas gets directed back through the gas tube.
5. Looking at averages, piston-driven AR rifles cost more. Now, you can certainly find some really expensive gas impingement guns, as well as some inexpensive piston-driven rifles, but the least expensive AR is typically a gas impingement model.
6. Whether you’re firing a gas impingement or a piston-driven AR, you will find it to be highly reliable. If I found myself in the middle of a post-apocalyptic world and had to choose between a gas impingement and piston-driven AR for survival, I would not have a strong preference either way. The main benefit I would see to gas impingement would be replacement parts: parts for gas impingement AR rifles are easier to find and more plentiful.
The truly good news is that if already have a gas impingement AR or a piston-driven gun and want to try the other one out, you don’t need to buy a brand new AR to do so. The upper receiver, the part that is either gas impingement or piston-driven, installs independently of the lower receiver, so it is just a matter of finding an upper receiver and swapping it out, and then you can try the other version out for yourself.