SIG MCX: When is an AR not an AR?

[El Mac]

In response, IIRC, to the MCX's accuracy... issues.

Pencil barrels do tend to have those...issues, particularly with heat induced from high rates of fire. No matter who makes 'em.

[Aries144]

At the rates of fire seen in semi-auto rifles with pencil barrels, heat more strongly affects performance by causing the Point of Impact to walk. You don't typically see groups open up very much until you start using full auto or doing multiple mag dumps. Aside from a "walking" POI, poor precision has more to do with the lack of symmetry in the bore and lack of consistency of ammunition. Other factors have no significant effect on precision until you're looking at sub minute shooting.

Making a barrel thicker does not equate to better precision, it reduces "walking." "Walking" isn't that big an issue in a 2 MOA or 3 MOA spec firearm if your barrels have a good heat treatment/stress relieving process. A thick barrel with an asymmetric bore will still shoot poor groups, the center of the group simply won't walk as much. A better solution to reduce "walking" in a firearm with 2-3MOA spec, that isn't expected to see much full auto fire, is to use thin barrels for weight savings and simply do proper stress relieving.

I suspect that MCXs sometimes shoot poorly either because Sig failed to require proper stress relieving and/or because they failed to tightly control the process that forms their barrels' bores. With Cohen's reputation for cutting quality control to cut costs, this doesn't seem far fetched.

A good demonstration of two barrels with good heat treatment and adequate bore symmetry is seen in this video, which showcases two AR15s using Faxon pencil barrels compared to an old Colt SP1 with pencil barrel. Faxon uses a process for their pencil barrels that nearly eliminates "walking" as the barrel heats and they're performing at 4ish MOA with a mag dump's worth of heat with the ammunition used in that instance.

[El Mac]

Walking, stringing, spreading...accuracy. Semantics.

The MCX was designed for a particular customer that wanted a weapon capable of full auto. They have the need. Based on feedback from them after 18 months or so of employment, the Virtus was "born" - or rather, the MCX was revised to include the heavier barrel. That customer was quite happy with the MCX. They are happier with the Virtus.

If one is into pencil thin barrels and mustaches, awesome and awe inspiring. Rock on.

[TacticalFun]

My snakebite got a friend.

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[Aries144]

Sure bud. If details and understanding why things behave the way they do don't matter to everyone, that's cool. But it's not semantics just because the terms were glossed over or not understood. The specific terms are distinct and important because they're different problems that need specific design solutions to address.

The main point is, stating pencil barrels all have accuracy issues is demonstrably incorrect. A heavy barrel is certainly still the best way to handle lots of full auto. The problem is that's not of any use to people who won't be firing their Virtus' on full auto and it adds a lot of needless weight.

[Beat Trash]

I had one of the original MCX's. Mine had stringing and accuracy issues that I would not blame on the pinnacle barrel. The issue would address itself when trying to sight in an optic. Slow fire, 3-5 round groups. By the third group, the stringing was occurring. In frustration, I dumped the gun. I later learned that the issue may have been with how the barrel was attached to the receiver, and if the bolts were torqued properly.

Yesterday I had a chance to briefly shoot a new 16" MCX Virtus. It was accurate and pleasant to shoot. A bit muzzle heavy but overall not bad. It made me wanting to shoot one of the 11.5" MCX's.

[mig1nc]

Shot my new MCX hybrid pistol 11.5 5.56 last weekend. Didn't have a ton of time, just four mags in about a half hour as I zeroed an EOTech EXPS-3 with a magnifier and tested a new trigger. Kept all rounds in the x-ring at fifty yard Target once it was zeroed. No complaints.

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[Beat Trash]

Shot my new MCX hybrid pistol 11.5 5.56 last weekend. Didn't have a ton of time, just four mags in about a half hour as I zeroed an EOTech EXPS-3 with a magnifier and tested a new trigger. Kept all rounds in the x-ring at fifty yard Target once it was zeroed. No complaints.

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Does your pistol have the factory brace on it? If so, does it fold flat?

[mig1nc]

So, I got a deal on it without the brace from a small gun shop because I knew I was going to rip out the AR adapter and put it on my SBR lower.

I have a Sig side folding stock on it now.

Pretty cool setup actually.

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[Nimslow]

So, I got a deal on it without the brace from a small gun shop because I knew I was going to rip out the AR adapter and put it on my SBR lower.

I have a Sig side folding stock on it now.

Pretty cool setup actually.

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That's where I'm going with my Rattler when my form 1 comes back. The SIG side folder. I may give the Parker Mountain Machine light weight stock a try.