I had my first failure in my MCX yesterday while closing in on 1k rounds fired since ownership. I started the day shooting wolf gold 55gr as has been the norm for the last few range sessions. This rifle has seen federal, LC and PMC xtac in everything from 55-62 with zero issues. When we loaded up Winchester 5.56 wth the NATO stamp I got a failure to extract from the bolt on almost every round which resulted in a double feed. I chocked it up to the extractor being gunked up as I have purposely gone without doing a real cleaning on the rifle (wipe down bolt is it and light lube). I throughly cleaned it last night and examined the extractor and spring and all looks perfectly fine. I cycled some LC, Wolf gold and xtac and it ejected just fine. It is still failing to extract the Winchester. I swapped out the extractor spring with a upgrade kit and black oring which resulted in the same exact results. The MCX refuses to extract the Winchester from the bolt. I figured this must be a ammo issue and cycled it through my mk18 with zero issues. So WTF?  Anyone experienced issues with the Winchester 556 before?

I only have 1K of Q3131A left, and it'll stay in an ammo case for when/if the SHTF. Nice, hot, and accurate ammo. It used to be the gold standard for 55gr 5.56. I'm sure there is better available now, but I'm nostalgic about this stuff.



You never mentioned which Winchester load. My experience with Winchester ammo has always been positive, I'd keep shooting it, and it should break in nicely soon enough. If not, you've discovered your MCX's Achilles heel.

It was this suff right here
http://www.luckygunner.com/5-56x45mm-55-gr-fmj-winchester-q3131-20-rounds
It's frustrating I can't figure out why the MCX won't eject it. My mk18 ejected it just fine. I'm going to try a different extractor on the MCX bolt next. The extractor on the MCX is more tapered than the more squared off one on my ARs. I'm wondering if that's the issue?

I don't know, in my opinion I doubt it's an issue with the ammo. Something needs to be tweaked within the MCX. It's not the same old Q3131A, but it is still a decent round.