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5/16/2026 9:14:25 AM EDT
[Last Edit: aftac][Edited]
What do I need to get the Sig regulator into a SIG MCX with a standard lower?  

Also I cannot tell if the Regulator rail is 9 inches or 10 inches.  

Are factory barrels the way to go or is cutting down the 16 inches barrel?  Anyone know how hard it is to change barrels in the McX?  

Just trying to setup an Sig CSAW but with a 10.5 or 11.5 depending on the rail.

Thanks.
5/16/2026 9:58:21 AM EDT
[#1]
Attached File
Attached File


Here is what I will be using.  Already have a Sig MCX two stage trigger in that lower.
5/16/2026 10:56:20 AM EDT
[#2]
You need the stock adapter

https://www.sigsauer.com/mcx-stock-adapter.html

This should be it.
5/17/2026 2:37:06 PM EDT
[Last Edit: SpyHawk][Edited] [#3]
[deleted, already covered]
5/17/2026 3:06:28 PM EDT
[#4]
I know I need the receiver extension, just trying to figure out if $1000 to turn my regulator worth it.
5/19/2026 11:37:42 AM EDT
[#5]
I have a Sig Regulator and I have a few extra Aero lower laying around. if I cut the barrel on the MCX to 12.3 inches I can still run the rail that came on the regulator. i might even go to 12.2 just for giggles. I looked at the price with a Spear-LT 5.56 my LE discount and its $2200 for the SBR.

If I build there are two ways do do it.
Buy 11.5 barrel $750-800
Buy lower adaptor $150
Buy buffer tube folding adaptor $100.
So $1050 after all is said and done.

Option 2
Cut 16 inch barrel to 12.3 $140.00 and lets say shipping $100.
Buy lower adaptor $150
Buy buffer tube folding adaptor $100.
So total $490.

Option 3 but a 11.5 upper for $1650
Buy lower adaptor $150
Buy buffer tube folding adaptor $100.

Option 4 buy a SBR Used Gen 2 or Gen 1 $1300-$2000 seems to be the going price on the used market.

Most of this is so I can travel more compact and to toss in my pack when I go backpacking instead of my CZ Scorpion. I might not do any of that and chest keep the CZ.

I am really looking for a folding stock 5.56 rifle from 12.5-11.5 upper.

I guess I could use a law tactical if I really want to do that but backpacking that can be an issue.


Let me know what people think and if I missed something with all the calculations.
6/22/2026 11:52:25 PM EDT
[#6]
Quote History
Originally Posted By aftac:
I looked at the price with a Spear-LT 5.56 my LE discount and its $2200 for the SBR.

View Quote


Check out SIG connect, I can get the 11.5 pistol for iirc 1900. Yes I pay for the SIG connect, at least a one plan and have just been buying the crap out of stuff right now. I also get a NRA instructor discount ( probably about the same as your LE price ) thru expert voice, but the connect saves even more.
"I am gonna laugh my ass off looking out the air vent of the box car watching some of you shot in the head in a ditch when you finally realize it's time to resist." stolen from RR_broccoli

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