MCX is sort of frustrating, but a pretty good system if you take the time to understand it. Sig has made a lot of (good) updates to mature the system and gets a lot of hate for all the changes, but it's not hard to follow and easy to avoid buying the wrong stuff.
So, I just bought a Sig MCX Virtus 11.5" 5.56, which took some searching in itself. I wanted to pick up a caliber X-Change kit, the 9" .300 BLK. Problem is... I have looked EVERYWHERE for a kit and it is nowhere to be found and the places I've seen have them say they are discontinued, I'm not sure if this is for the 1st gens or the Virtus models... I also got the urge to pickup an MPX in the 8" varient (which I don't think Sig even makes anymore now), so I looked for their 'new' 4.5" version which is nowhere to be found either. Then they come out with this new copperhead which is not my cup-o-tea. Can someone in the know fill me in on what's going on with the ever changing product line?
Couple things are confusing about the MCX. It has undergone a number of revisions but can be oversimplified into three civilian product lines:
-Gen 1/1.5 "Legacy." Recognized most easily by the pencil profile barrel and longer top receiver rail. Gen 1 had the first pattern (square lug) bolt that looked a lot like an AR15 without the tail. They also have a neat tensioning plunger in the lower to hold the upper on tightly. Sig did a an upgrade program on these where they replaced the bolt/barrel/carrier/charging handle to "Gen 1.5" which had a rounded lug bolt and new safety bar on the carrier. NOTE Gen 1.5 ended compatibility with most aftermarket AR15 triggers not made specifically for MCX. You'll occasionally see "G" marked carriers that are compatible with Geissele AR15 triggers.
-Virtus (current). Flagship product line. Probably called the "Virtus" to separate it from the previous MCX line as a lot of it is not compatible. Barrel profile became heavier and gas system length changed a little. Upper receiver rail is shorter. All bolts are the current "tapered, rounded lug" pattern. Tensioning plunger deleted. I think also some profile changes on the receivers.
-Rattler (current). Virtus-type bolt and will accept virtus barrels, but at least the gas system and recoil assembly are different. People complain about this, but I do not see any way they could have gotten the rattler as small as it is without reducing stuff. This was designed specifically for a contract solicitation and it seems that Sig is amortizing the cost a bit by offering it on the commercial market.
Compatibility notes:
-Gen 1, Virtus, and Rattler rails are all different and they won't fit each other. Pay attention to what you buy.
-Gen 1/1.5 bolts and barrels cannot be used with a rattler/virtus bolt/barrel as they won't fit the receiver extension. If you're going to put a virtus barrel on a legacy gun, or vice versa, you'll need the right bolt for it, too. Somewhere there is a picture of all three side by side.
- Gen 1, Virtus, and Rattler gas system lengths are all different. Virtus barrels can be used on Gen 1 rifles, and vice versa as long as you have the right bolt, but the gas port switches will not line up exactly with the holes in the receiver.
I'm just concerned that the MCX is going to turn into another Masada/Magpul/Remington ACR.
At this point, highly unlikely this is going to happen. A lot of military and LE organizations (here and internationally) have adopted the MCX in some form or another. I think this may be partially to blame for the availability problem. I'd say the MCX is here to stay.
The 300 blackout kits caliber exchange kits have never been available, pure vapor ware
I've had three in the last two years, they are around and you may have to backorder.
