1 Feb 13
At an Urban Rifle Course in South Florida earlier this week. I ran my XCR-M in 7.62×51 (308 Win) for two days, and several of my students were using gas-adjustable rifles as well.
Some gas-piston rifles, like the ever-popular M1A, are not gas-adjustable, but many others, like the FAL, SIG/556, and the XCR-M, are.
Variable gas adjustment enables the user to tune his rifle to best take advantage of the particular ammunition he is using, by selectively venting excess gas, still insuring normal operation, but attenuating recoil and wear-and-tear on the rifle itself.
That all works fine when you’re consistently running a particular kind/brand/lot of ammunition exclusively, but it becomes a problem when magazines are routinely charged from a “grab-bag” of mixed-together rounds that were scrounged-up and deposited in a catch-all box! With the currently escalating price of ammunition, such “grab-bag” shooting/training sessions will become ever more common!
I was running my XCR-M on the “#3″ gas setting, and it was functioning and spitting-out brass normally. The XCR has five gas options. “S” (for “suppressor”) vents-off nearly all the gas. On the other end of the spectrum, the “#4″ setting vents almost no gas, so nearly all of it goes toward running the piston. Settings one, two, and three are in-between.
As noted, #3 was running fine, until several cases failed to fully eject and hung-up in the ejection port. To be fair, it took over a hundred rounds for the issue to manifest itself. I was indeed using a random mix of ammunition. Changing the setting to #4 cleared-up the problem immediately. We call this maximum gas setting (#4 in the case of the XCR) running “wide-open,” that is, almost no gas vented-off. You also experience maximum recoil!
However, running wide-open pretty much assures your rifle will run normally no matter what you’re feeding it.
My African friends routinely run their FALs wide-open, not willing to risk even an occasional short-cycle.
In any event, I’ve decided to leave my XCR on #4 for now, not knowing what I’ll be compelled to shoot through it in the near future.
The point here is that we have to run our gear, and ourselves, regularly and hard! Little issues often don’t rear their ugly heads when we just casually shoot a few rounds, occasionally, and outside a genuine training environment.
When the real Test comes, we have to have gear we can trust. Our lives depend on it!