When Did the Direct Impingement AR15 Become So Reliable?

The subject of piston AR15s recently came up during a meeting of Lodestone staff. This is a topic that has fallen off the radar for many, but with so many new AR15 owners it seemed like a good time to discuss the reasons behind their initial development, and why they’ve fallen out of favor. Please keep in mind this article is not an exhaustive study of the development and history of the AR, and it is written from the perspective of the author, who writes from his own experiences and biases which may differ from yours.

For those who don’t know, the piston AR15 was sought out as the solution to the reliability shortcomings (some real, some perceived) of short barrel ARs in the late 90s and early 00s. In the early 2000s it was accepted gun lore that a direct impingement (DI) gun would get you “killed in the streets” and that piston ARs were the future. Yet in 2020, the short-barreled DI guns reign supreme in the US, except for some Special Mission Units. Why? Have you ever seen the meme that shows the Kardashians and states “you’re not ugly, you’re just poor”? Same thing for the short-barreled DI guns – they weren’t unreliable, they just suffered from a lack of development. So, what were these developments? Most of them were designed to overcome the more violent operating cycle of a short-barreled AR compared to a full-length rifle like an M16A2. In no particular order, I believe you can trace the increased reliability and thus increased acceptance of short barreled ARs to the following:

The acceptance of lubrication as playing a role in reliability. For a long time “a thin coat of CLP” was the answer. Now, it’s understood that “wetter is better”. Anyone who has attended a carbine course can attest that dry guns go down more frequently than lubed guns.

The increase in the weight of the buffer. Early on, in any short barreled DI AR you had one option – the carbine buffer. Now we have H1, H2, and H3 – each heavier than the last. A general rule of thumb is to use the heaviest buffer that will reliably lock the bolt back on the last shot.

The addition of M4 feed ramps to the upper receiver. Unless you’re a real nerd you probably don’t remember when extended feed ramps hit the scene. By creating a longer and less abrupt path for the round to feed into the chamber, it cut down on the frequency of stoppages.

The development of a stronger extractor spring. Depending on how much of a nerd you are, you may not remember the talk of blue insert vs black insert extractor springs. Bottom line is, the black insert identified the newer, stronger extractors springs designed for the more violent operating cycle of the short barreled ARs.

Finally accepting that a magazine is a consumable wear item with a lifespan. I am of the firm belief that many, many cases of poor AR reliability can be traced back to using worn out magazines. For whatever reason – from bureaucratic cheapness to the 94 AWB – people held onto their magazines like cherished heirlooms. Accepting that these mags have a finite life span was a huge step forward.

Building upon that, the development of anti-tilt followers by Magpul and others also played a big role. The original USGI 30 round mags had black followers, which were replaced with green followers, and then Magpul’s self-leveling followers exploded onto the scene. Again, a little tweak needed to compensate for the more violent operating cycle of a short-barreled AR.

The PMag’s contributions to overall reliability cannot be overstated. A great deal of thought went into the magazine and besides having a self-leveling follower, it was also designed to have a constant curve geometry which ensured smooth and reliable feeding of rounds. Additionally, they are inexpensive and easily mass produced, all of which make people more likely to toss them when and if they reach the end of their service life.

Free floated rails. This may seem a bit of a stretch but there is evidence that free floating rails help aid in reliability by extending bolt life.

                All those relatively minor changes added up to major reliability increases in the DI guns, while still being cheaper and lighter than the piston guns, which have their own set of issues. Everything mechanical has a failure point and you can’t get something for nothing. My suggestion? Rather than engaging in debates on the internet about these things, grab your rifle and take a carbine class and see for yourself.

—Flynn