AR15 Basics – D.I. vs Piston System


There seems to be quite a debate going on recently about what is a better gas system for the AR platform. So we’re going to take a look at a few of the basics concerning these two very different gas systems and compare the two and hopefully help you, the end user, decide what will work best in your rifle.

First off we have to acknowladge that the AR platform was designed to work with the Direct Impingement gas system and that for the most part Piston Systems are basically just add-ons or adaptations of the original DI designed rifle. It’s basically a modification to turn a rifle designed to work properly with DI into a piston rifle.

Some area where the DI system outshines a Piston system are as follows ……..

Free Float barrels – This is an obvious one, basically even though you can technically free float a piston rifle, it makes little sense as your negating the purpose of free floating a barrel by adding a moving piston that connects the barrel to the receiver.

Less Moving Parts – Again, pretty obvious, but it’s worth mentioning. Less moving parts equals less parts to have issues with.

Lighter weight – Self explanitory, although a few ounces shouldn’t make or break your purchasing decision.

More Common – This equates to easier to find and cheaper to purchase parts, along with more compatability with other rifles that might be used for parts interchangability.

Accuracy – This is another area where it should be obvious that by having a moving piston adding recoil, right above your barrel, your going to loose accuracy, especially for follow up shots.

Cost – Obviously because of its commonality and because its usually the way a rifle is manufactured, the cost is significanty less than that of a piston system.

Industry Standard – This comes into play because at this time there really is no industry standard for piston systems like there are for DI system rifles. There are many good companies that manufacture high quality piston kits or rifles designed to function with a piston system, but those companies do not all manufacture their kits and parts to be interchangable as every other part on an AR platform rifle is.

Now lets look at a few areas where the Piston System does a particularily good job ……..

Cleaner running & Heat Resistance – This is the biggest and most obvious advantage over a DI system on an AR platform rifle. The biggest downside to the DI system is that it dumps hot gas and fouling into the action of the rifle and the piston system takes care of this problem by venting all the gas elsewhere making the rifle easier to clean and require less maintenance and cleaning.

Reliability – Because of the issues with the DI system fouling up the action a case can be made that a Piston system is inherently more reliable than a DI system because fouling and carbon build up do not enter the action and potentially cause reliability problems.

Suppressors – One reason suppresors tend to work better with Piston systems is because the nature of a suppressor restricts gas coming out of the muzzle and with a DI system all that restricted gas that would normally be blown out of the muzzle gets directed back into the action and not only causes even more fouling than normal but has also been known to cause excessive gas to come out to areas of the receiver like the charging handle area and blow gas into the face of the user. For this reason a Piston system, which drastically cuts down the amount of gas that is distributed into the chamber, is perfered for rifle fitted with suppressors.

SBR – Piston systems also tend to function very well on Short Barreled Rifles because of the higher port pressure, making Piston systems popular on barrel lengths shorter than 16″.

Running Dry – The piston system is much more capable of running on a dry chamber and action as opposed to a DI system that requires much more lubrication to continue to operate efficiently due to a high rate of carbon build up and fouling distributed into the action of the rifle.

So those are the pro’s and con’s of Direct Impingement vs Piston Systems on AR platform rifles.
In the end, for most civilian shooters, the differences are negligable and either system will work very well for just about anything you will ever use your rifle for. It really comes down to personal choice.

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