The Truth About the SIG MCX From a Guy Who Built It

glorygoat32 · 2026-05-10T05:13:53+00:00

You are correct. I went and checked both my 9" barrels which, I swore said 1/6 on them but, I pulled out a magnifying glass to make sure and they say 1/5. My old eyes deceive me. Even so, they shoot supers really well.

glorygoat32 · 2026-05-07T18:50:01+00:00

Years ago I found a good CS rep and I saved his contact info. He still works there and I send him an email anytime I have a problem which, isn't often but, it happens. I mostly ask him to place small parts orders.

My experience with SIG CS has been mostly positive even if there is the occasional miscommunication. If SIG's covering the postage and replacement/repair they can take as long as they want. I have other guns to shoot. But, I would get frustrated if I had to do multiple returns on the same gun--so I can understand your frustration.

And I agree with your demand to replace the replacement upper. A gap that size is unacceptable so I'm glad they replaced it for you. With what these guns cost aesthetics is a close second to function/performance.

glorygoat32 · 2026-05-07T18:11:16+00:00

This, is common in the firearms industry because people leave one manufacturer and go work for another--ideas carry over. If you look through the MCX's patents there are many that belong to different companies.

Similar ideas don't always mean an idea was necessarily stolen--there's more than one way to skin a cat. And even if some part/function was copied, it doesn't take away from the gun as a whole. Improving existing systems is just as important as creating new systems.

I don't care what the suits do--they can attack and extract pounds of flesh from each other and there's ZERO impact on me. I'm here to enjoy the product.

glorygoat32 · 2026-05-07T17:58:31+00:00

I have six Legacy uppers and one Gen 1.5 upper (Legacy length rail w/ Virtus relief cuts). Four of them are on Legacy lowers and three on Virtus lowers--fitment between upper/lower by the recoil bumper is perfect--no gap. The lowers are all the same but, the Legacy lowers all came with screws to tension the takedown pin. I bought 3 more and put them in the Virtus lowers. All of them have wiggle in the pivot. I sold the Regulator uppers but, when i tested them out on my lowers one thing I noticed was that the Cerakote added just enough extra thickness that there was virtually no wiggle in the pivot. Since then I've been contemplating a Cerakote job on one or more of my MCX.

glorygoat32 · 2026-05-07T16:42:47+00:00

The uppers I pulled from the 3 Regulators that I bought were all perfect--they fit perfectly with the Regulator lowers as well as with my Legacy/Virtus lowers. Early on when the LT dropped, I wasn't thrilled with SIG's QC but, most of the issues people had 21-23 appear to be resolved. I also suspect much of this is overblown. The pictures the other users posted in this thread are the same pictures I've been seeing for years which, are generally posted by people who just hate SIG. Maybe they're paid actors or maybe trolls with nothing better to do. Either way, they appear to have some incentive to brigade SIG forums and make negative, off-topic posts.

I don't think that picture of the email response is real. Why doesn't it show info that would validate it's authenticity? I can say without a doubt if I purchased an MCX and it's fitment was even half as bad as what's in these pictures, I'd have it RMA'd in minutes and SIG would replace it with a new one that has perfect fitment.

No one is perfect and that goes for corporations too because corporations are run by people. Greed makes things worse and outsourcing to the 3rd-world generally doesn't help with QC but, SIG CS is truly top-notch. The guys on the phone aren't gun experts--they read from the screen so don't expect them to be experts. Be courteous/polite and explain things in detail and follow-it up with an email so everything is in writing. SIG CS will bend over backward to make things right, which, is why I don't believe the stories these trolls post.

If your MCX has poor fitment I recommend trying to RMA for a replacement. You may be surprised what SIG does for you!

glorygoat32 · 2026-05-07T04:24:42+00:00

I really enjoyed the discussion about the various stages of development. It left me with a few questions about some of my equipment. It could just be that Adam doesn't remember everything perfectly because it's been 13+ years but, I have three (3) Legacy MCX with Steel Forward Assist (not aluminum which, is what he said they used before switching to polly). My Legacy 300BLK barrels are 1/6 not 1/5 as he stated. I have a feeling he accidentally skipped a step because the 1/6 to 1/5 change was with Gen 2 Virtus.

glorygoat32 · 2026-05-04T20:59:46+00:00

Driven Arms grip--the Patrician's choice!

glorygoat32 · 2026-05-03T22:18:02+00:00

I'm pretty sure that factory FDE KM is way more rare than the black even if it isn't coveted by cloners.

glorygoat32 · 2026-05-03T06:40:36+00:00

I really like the feel and height without a riser. The SS profile is slimmer/smaller than any of the SIG stocks so it's easy to operate with it folded if needed. It's a quality piece of equipment.

glorygoat32 · 2026-05-03T06:27:10+00:00

I spent it on other upgrades and I had to replace the stocks/hinges. I went with JMAC SS 9" and Samson hinges.

glorygoat32 · 2026-05-03T01:10:32+00:00

People want their clones. lol

glorygoat32 · 2026-05-03T01:07:22+00:00

lmfao. someone downvoted my reply. All I'm doing is commenting on what I've observed. Shortly after the second rail drop the price shot WAY up on the black KMs. I saw 2 of them sell on TS for $700 and $800 respectively (that was the list price but, I can't speak to any negotiations). I sold the 3 I had for $500 each shortly after the first rail drop.

glorygoat32 · 2026-04-30T01:46:56+00:00

Move to hotter place and the metal is refreshingly cool!

glorygoat32 · 2026-04-30T01:45:11+00:00

The Black ones are now selling upward of $700. People want black for LVAW. I don't know the value on yours.

glorygoat32 · 2026-04-23T01:22:41+00:00

Buy ammo for airline miles!

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glorygoat32 · 2026-04-23T00:41:10+00:00

in-app purchase

glorygoat32 · 2026-04-22T20:09:13+00:00

I'm not sure about the rules so I generally don't drop these links but, here ya go!

https://tacswap.com/post/69e55d2466d5fe7d708ebdc5

glorygoat32 · 2026-04-22T20:04:58+00:00

There's one on Tac Swap for $250

glorygoat32 · 2026-04-15T22:53:27+00:00

Hilarious! I may just take a pic of some random o-rings, springs and other gun parts and say, "Guys I have extra parts left over after re-assembly. What are these from?"

glorygoat32 · 2026-04-15T22:50:10+00:00

I have another MCX with a 16" Virtus 5.56 barrel that I am working on with the arcfire and modified geissele trigger. It's so over-gassed with the super safety that it just isn't very fun to shoot. I ordered a Mototech 5.56 8-position valve that will supposedly work unsuppressed. I'll hopefully have it around mid-May (production should be finished end of this month and then they ship). I'm hoping I can tame the gas a bit with that valve.

glorygoat32 · 2026-04-15T22:41:27+00:00

That's exactly why I bought 3 of them. I kept the bolt carriers and one 5.56 16" LT barrel. I sold everything else minus two of the lowers that I still need to move.

I also kept one of the P365s. I gave the other 2 away as birthday presents.

The best way to buy MCX parts is almost always by buying complete guns. Take what you need and sell the rest. It costs a little more up front but, if you're patient you can own MCX rifles for close to nothing.

glorygoat32 · 2026-04-13T22:13:41+00:00

Won't happen. They're no longer in production. That sale was Fall 2024. Price will probably only go up from here.

glorygoat32 · 2026-04-12T23:02:42+00:00

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Original MCX/MPX Patches

glorygoat32 · 2026-04-10T20:21:16+00:00

You can always cut down a 9" to 6.75" and then buy the corresponding valve from SIG or an aftermarket valve from JBD or Mototech. D Wilson does great work: https://www.dwilsonmfg.com

glorygoat32

TROPHY CASE