Gas markings on MCX

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March 30, 2017, 01:48 PM
Bart Noir
Gas markings on MCX
I recently bought an MCX which has been desired since it first came on the market.

And within 3 hours I was aware of the recall. but that is another story and it is proceeding along.

But the markings for the gas selector do confuse me. I read that early ones had a "U" and an "S". Then these were changed to a "-" and a "+". That is what my manual describes.

But I cannot find any of those markings. And I have looked carefully all over the area around the selector. All I can find is something on the actual selector. It looks like a fixed indicator mark and then on the rotating selector, there appears either a COI or C0I. The indicator mark lines up with the C when I have it set to what I think is the "extra gas" setting. It lines up with the O or 0 when set to what I think is the "normal gas" setting. But I might have those reversed since my manual is of no use in describing the settings.

The answer might be in the new edition of the manual which should be accompanying the replacement Bolt Carrier Group, or whatever SIG calls it.

Does anybody know of this version of labeling?

Bart Noir
March 30, 2017, 07:16 PM
The indicator markings are on top/side of the rail just behind the adjustment.

"+" is the Adverse setting (or Un-Suppressed), "-" is Normal ( or Suppressed) for 5.56mm cartridges.
April 04, 2017, 01:47 PM
Bart Noir
I've again examined my MCX and the rail is totally without markings.

I guess I have no problem with that since there are only 2 choices of gas settings. If I can't figure out which is optimal for my non-suppressed carbine, then I probably shouldn't be handling a firearm at all!

Bart Noir