SIG MCX: When is an AR not an AR?

[interfan]

The first batch of new 11.5" MCX pistols shipped last week and are now showing up on GunBroker. Hopefully this means that factory short barrels are not too far behind...

Hopefully very soon...

[FlyingChipmunk]

I'm hoping for the .308 version one day.

I think Sig's submission for Army's CSASS was basically MCX in /308

[Auto426]

I think Sig's submission for Army's CSASS was basically MCX in /308

Pretty much. The CSASS submission was basically an enlarged MCX that had a non-reciprocating folding charging handle added to the left side of the gun. The design looked very promising. I was hoping we would see it at SHOT this year but it was a no-show. Hopefully they continue to develop it for the commercial market and not just shelve the whole project.

[ABNAK]

Shot mine for the first time today. 83 rounds total. No function hang-ups at all (FTF, FTE, etc.). Mostly M855 but 20rds of IMI "Razor" 77gr (Israeli Mk262 clone). Had a lot of failures to lock back on an empty mag; the more I shot the less frequent they became but by the time I was done it was still occasionally occurring. I'm not overly concerned with that issue but when cleaning afterwards I noticed the spring resistance on the mag catch wasn't very strong......may have to replace that. I was using an Aimpoint T-2 from a sandbag to zero at 50yds. Wanted the rounds just a c-hair low (maybe a 1/4 inch or more) as the height-above-bore is greater than an AR so it would maintain the approximate trajectory of the 50yd IBSZ. For my 50yo eyes and with no magnification it is a 3-4 MOA gun. Certainly not stellar but with magnification I'd guarantee it would be better (and probably without ME shooting it!). It is in line with my other AR's with RDS accuracy-wise. Certainly acceptable for "combat engagement" ranges. Recoil impulse, as with most piston weapons, is abrupt but it is s-m-o-o-t-h! I definitely like the way it feels.

I had done the mod a page or two back where my buddy milled a slot in the rail right over the gas block's exhaust port so the residue would blow out the hole as opposed to building up under the rail, which is a tough spot to get to when cleaning an MCX (without removing the barrel of course). I decided to see just how much crap this allowed to escape by holding a piece of paper over the slot. Below is the result after just three rounds. Obviously I let it slip for one round but you can see that the slot allows the vast majority of residue to vent upwards out of the rail.







Bottom line? I like this gun. I'll eventually conquer the lock-back issue but otherwise Sig did good on this venture in my book. Just wish that damn rail was less tall and more streamlined, at least as much as you can with a piston.

[WatchTheWorldBern]

Wait, does the MCX really have a different optic/sight height over bore from an AR? That's honestly pretty surprising to me.

[vereceleritas]

Wait, does the MCX really have a different optic/sight height over bore from an AR? That's honestly pretty surprising to me.

Shouldn't be a surprise as that's the case with most piston guns. The SCAR, MR556, ACR, and Tavor are the same way. Need the extra room for the oprod, I guess.

[mig1nc]

Has anybody measured the difference in the rail height over bore?

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[ABNAK]

Has anybody measured the difference in the rail height over bore?

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I keep my gun room locked up during the work week. Tomorrow night I'll open it up and take a look. I made the mistake of trying to measure from the center of my Aimpoint T-2 (with a lower third co-witness so that adds to the height) to the center of bore. Of course back over the receiver area you are guesstimating about where the center of bore is. Tomorrow night I will flip up the front sight and measure from the top of the front sight post to the center of bore and report back.

[mig1nc]

Cool, thanks. Let us know rail height too if you have the time.

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[ABNAK]

Cool, thanks. Let us know rail height too if you have the time.

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Okay, the distance from the center of the bore to the top of the front sight post is approximately 2.9". The distance from the center of the bore to the top of the picatinny rail is approximately 1.55".