In case you don't want to read the whole article copied from "Defense Review".
It’s up against the growing skepticism and doubt about the supposed superiority and/or advantages of gas piston/op-rod ARs over traditional direct-gas impingement (DGI) a.k.a. direct-impingement gas (DI Gas) system AR-15 carbines/rifles. with regard to weapon reliability. There are a couple of important points to be made about this. First, as we’ve already pointed out in a previous article, there are a number of very knowledgable people out there, including, but not limited to, tactical AR-15 builders out there like John Noveske of Noveske Rifleworks, LLC and Nathan Roads of Next Generation Arms (NGA) and professional military Spec-Operators (including U.S. military Special Forces and Special Operations personnel) that actually prefer the traditional DGI setup over the gas piston/op-rod setup. Not do traditional direct gas guns tend to be more accurate, lighter-weight, softer and smoother shooting, and mechanically simpler than gas piston/op-rod guns, but there is now growing evidence that they may be as or more combat-reliable than gas piston/op-rod guns, provided the DGI guns (like the Colt M4A1 Carbine, for example) are “sprung right“, are properly maintained, and have a barrel of at least 12.5 inches (12.5″
in length. A direct-gas AR-15 SBR with a 12.5″ barrel can retain and utilize the standard M4/M4A1 Carbine-length gas system, thus optimizing weapon reliability. Piston guns are easier to clean/maintain in the field since they don’t get as dirty inside. However, the “crud” that builds up inside a DI gas AR at high round count is not what causes reliability problems.
Remember, the reason that a certain U.S. Army Special Forces (SF) unit chose the HK416 piston-driven platform was because they wanted a short weapon with a 10.5-inch (10.5″
barrel that would run reliably with a muzzle can (silencer/sound suppressor). A gas piston/op-rod setup doesn’t rely on barrel length to create the necessary gas pressure curve and timing like a direct-gas-impingement system does, so you can cut the barrel down to 10.5 inches with no loss in weapon reliablity. However, if you’re willing to go with a barrel length of 12.5 inches and up, it’s questionable that a gas piston/op-rod gun offers ANY reliability or durability advantage whatsoever over a direct-gas gun, even with a suppressor attached.
In fact, there’s now some evidence to the contrary, since the much vaunted and supposedly superior HK416 has been running into some rather serious reliability and durability problems in the field as of late, including the piston system locking up in cold weather and the upper receiver cracking. And, the HK 416 is supposed to be the most combat-proven gas piston/op-rod AR out there! According to some unconfirmed/unverified reports Defense Review has received from some of our industry contacts, the HK-416 receiver-cracking issue has led to U.S. Special Operations personnel operating under SOCOM (USSOCOM) to switch out their HK416s with combat-proven Colt M4A1 Carbines, so they’re now back to using combat-proven direct-gas-impingement guns. The fact is, the Colt M4A1 Carbine is truly combat proven, and significantly more so than ANY gas piston/op-rod AR out there, including the HK416.
