Direct Impingement & Gas Piston Systems

Here at Gunbuyer we frequently receive questions from prospective gun buyers like, "What’s the difference between a piston rifle and a direct impingement rifle?"


Direct Impingement

A DI, or Direct Impingement rifle, is a rifle that uses the gas from a fired cartridge to assist in the cycling of the rifle’s bolt. The fired shell is extracted while the next round is stripped from the magazine and seated into the bolt so that the rifle can fire again. This method of operation was made famous by Eugene Stoner when he designed the AR15, eventually being fielded by the US armed forces, commonly referred to as the M16 rifle.


Direct Impingement SystemDirect Impingement


Towards the end of the barrel is a small hole. When a round is fired the gas that pushes the projectile out of the barrel makes its way to that hole. The gas is then bled into the hole, connected by a gas block which is connected to a smaller tube. This will direct the gas back into the bolt (or in the case of the AR15 the bolt carrier group.) The bolt carrier group is then pushed to the rear of the rifle thereby completing the cycling of the bolt so that the rifle will fire again when the trigger is pulled.


Direct Impingement gif


Some of your most common examples of a direct impingement rifles are the Smith and Wesson M&P Sport II rifle, BCI Defense AR15 rifles and your Daniel Defense line of AR15 rifles.


Gas Piston System

Piston rifles operate similar to direct impingement rifles but the main difference is when the gas is redirected into the gas tube, instead of blowing back into the bolt carrier group, it is instead captured by a rod or piston which uses the force of the gas to push the bolt back. This in turn extracts the round and cycles the bolt so that the weapon can be fired again. Some examples of a piston rifle would be the Springfield Armory M1A, Sig MCX Virtus and Sig 516 rifle or most recognizably the AK47 rifle.


Gas Piston System


Piston vs. DI

Each system has its own benefits so you will need to decide which method will work best for you and your application. One of the biggest benefits of a direct impingement rifle will be the ease and low cost of replacing parts if you experience breakage or damage. DI is a proven platform with a multitude of manufacturers so if the need to replace parts arises they can be found readily at a reasonable price. One downside to a DI system is that with the gas blowing all the way into the bolt carrier group it can heat up the bolt carrier group and potentially cause more fouling due to the amount of gas entering the chamber.


A piston rifle will generally run cleaner than a DI rifle because the piston is doing the lion’s share of the work in cycling the bolt. As the bolt moves the gas is being bled off so hardly any gas will make it to the bolt carrier group. This will also leave the bolt carrier group to operate at a cooler temperature than a DI rifle would. The downside to a piston rifle will be the cost of replacing parts. Most piston rifles use proprietary parts so should something break you would have no choice but to get your parts from that manufacturer.


Piston System
Gas Piston System


With this information provided I hope this will be helpful in you deciding which rifle plan to acquire in the near future.  As always if you have any questions feel free to reach out to us at 855-318-4867.


Credit: B. Hawkins