Direct Impingement vs. Short Stroke Piston Systems
Ok, folks, here I go. Yup, I am going to open that can of worms to find out what’s the best carbine. First I’ll say that I am a fan of both operating systems and both will work well as long as you purchase your gun from a quality firearms maker. The gas direct impact system was first introduced in the AR format in the early 1950s by a man who needs no introduction in our community…Eugene Stoner. What a kick ass assault rifle that was in its day! It was used by Navy SEALs in Vietnam and quickly became the weapon of choice for the Men with Green Faces. The short stroke piston was used by a name that might be familiar to some…Mikhail Kalashnikov and his AK-47, the most widely used assault rifle in the world.
The AR is a self-loading rifle that performs a basic set of functions without manual assistance from the operator. After the trigger is pressed, the gun fires a cartridge, extracts the fired case, ejects it, picks up a fresh cartridge and transfers it from the magazine into the chamber, locks the breech and cocks the hammer to return the rifle to battery with a round in the chamber. It’s really a straightforward mechanical operation, and there have been a variety of ingenious solutions to this over the years.
Two of those solutions for the best carbine are the direct gas impingement system and the short stroke gas piston system. Eugene Stoner utilized the impingement system in the AR. It works by bleeding propellant gasses through a port at the end of the barrel and channeling the gasses back through a tube to directly strike, or impinge, a bolt carrier, thereby pushing it rearward to extract and eject the fired case. As the case is propelled forward by a spring, a fresh round is stripped and pushed into the barrel’s chamber. The direct impingement shines in longer barrel (18″ and up) applications where accuracy, particularly at longer ranges, is the goal. The simplicity — light weight and low cost for the standard parts — of the direct impingement system makes it the choice for most non-full-auto applications.
A short stroke gas piston system is what Mikhail Kalashnikov used in his AK-47. The piston system also relies on propellant gasses that are bled through a small hole in the barrel, but instead of the gasses traveling through a tube to impact a bolt carrier, the gasses are contained in a cylinder in which there is a piston. The gasses push the piston, which in turn is connected by a rod to a bolt carrier that moves to the rear to extract and eject the fired case. Moving forward from spring pressure, it strips a fresh round from a magazine, chambers it and locks into battery. The gas piston system shines in short barrel (e.g., under 16″) applications. The high port pressures found in short barrels can quickly erode the gas port. A well-designed piston system can accommodate the changes in port size. For much the same reason, gas piston designs can be more tolerant of suppressors. The advantages also increase where full-auto is concerned.
Finding the Best Carbine
Let’s hit some quick pros and cons on these systems as you try to determine the best carbine to protect you and your family. I know there are more, but I think these are the important ones:
Direct Impingement Pros:
- Free floated barrels are practical; the gas tube is the only (very minor) exception to floating free
- Simple construction, inexpensive, nothing to wear, foul or corrode
- In the AR, ready availability of standard parts at extremely competitive prices
Direct Impingement Cons:
- Sensitive to ammo variations
- Much of the spent gas ends up inside the receiver
Gas Piston Pros:
- Spent gas is vented externally
- More tolerance of ammo variations
Gas Piston Cons:
- Can’t free float to the same degree as direct impingement
- More complex, more parts to foul, corrode or go bad.
- Much more expensive
- No standard, every system is different
And the Best Carbine is…
Alright, we’ll call it draw. If you don’t regularly fire 1,000 rounds or more in a session, especially if it’s not full-auto, and you have a civilian-legal barrel length, you may well be better off investing in more ammo, paying for a professional carbine course and becoming more proficient with your direct impingement system than spending the extra money on a gas piston system. I have to say that this will be the case for 99% of civilian shooters.
On the other hand, if you’ve got a bunch of cash burning a hole in your pocket or if you tend to fire on full-auto when practicing for the inevitable zombie attack, then gas piston will be your best bet. No matter which one you choose, make sure you always practice safe weapon handling, do lots of dry weapons training and keep your bang-stick clean.
Leave a reply below to share your thoughts and experience with either of these systems. After you’ve done that, let’s go shooting!