As part of their recent set of mud testing, including some disappointing results from the fabled M1 Garand, and AK rifles, Ian and Karl of InRange have tested a weapon most people would expect to wither like a delicate flower at the first frost, in the presence of mud: The AR-15, designed by Jim Sullivan, and based on Eugene Stoner’s innovative, but maligned direct gas impingement operating system:

A shocker to some, but maybe not to others: The infamously “unreliable” AR-15 passed. One thing Ian and Karl did not mention which is a huge boon to the AR-15’s reliability in situations like this is the very thing it’s most often criticized for: It poops where it eats. Rather, the specific brand of direct impingement gas system that Eugene Stoner designed vents gas at the bolt carrier through two small ports. This gas vent acts to a certain degree like a compressed air hose, blowing dirt and debris away from the action before it has a chance to be carried back into the sensitive moving parts group. Further, the fact that there is a sealed gas tube, with no operating rod trying to move forward and back through it means that it’s extremely difficult to get debris into the heart of the AR-15’s operating mechanism.

Many of our readers expressed shock that the AK, a weapon described as having “legendary reliability” often enough as to make one nauseous, did not perform perfectly in the same test. While the gun did not stop functioning, it failed to continue operating in a semi-automatic fashion. This led many to conclude that the test was simply too difficult for any rifle to pass. Those of us (myself included) who have performed this kind of testing on AR-15s previously, however, knew that the AR-15 passes tests like these with flying colors, and the results of the InRange test surprise me not at all.