I see these MCX "hybrid" pistols on gunbroker, which looks like they have MCX uppers on M400 lowers, but I can't find them on the sig website. What's the story with them? I'm looking for a 9" 300blk upper to go on my lower (after appropriate tax paid to the Crown, of course), and this seems about the only way to get one.

Any insights?

https://www.gunbroker.com/item/757339242

Thanks!

If I'm not mistaken that is the same company that was selling the MCX uppers and lower separately a few months ago.

If you bought them both from them it was a few hundred dollars more then just buying the whole gun.

I have one in transit and will let you know when it gets here, although I bought the 11.5" pistol version and then bought a 6.75" 300BO barrel kit (hopefully its a Virtus kit with new bolt) to go with it.

It will go on a Colt lower that is SBR'd.

I did get a lot of info from a guy on the Sig MCX FB group. I also have one arriving at my FFL today. I intend on SBRing it and putting on of the Sig QD suppressors on it. Paperwork is ready to go. I am going to use my current MCX lower for the SBR, then I'll use the M400 lower to build something else from. In the meantime, I can play with it as a pistol until the permission from the Crown is received to make it an SBR.

finally picked up my Hybrid, I was waiting for my P239 Tactical shipped separately to arrive so I could do one 4473 for both but looks like it was stolen while in the care of the USPS.  I guess the govt. does need better gun control.

anyway, I purchased the Hybrid 5.56 pistol with 11.5" barrel.  I can post pics upon request.  I also purchased a Virtus 6.75" 300 BO barrel kit which came with the updated Virtus bolt.

Some observations before I take it to the range.

I was hoping to get the updated Virtus charging handle based on some examples I had seen on gunbroker, however I got the original generation handle.  I went back to gunbroker and looked at the minority of auctions that didn't use canned pics.  It seems that the updated Virtus charging handle appears on .300 BO pistols and rifles.  I didn't see any examples on 5.56 guns but its a small sample.  Mine was mfg. in Dec 2017 if that makes any difference.

Handguard is too small for a suppressor so it won't work with my 300 BO barrel kit.  Not a big fan of how the keylok handguard looked anyway, looks like some cheap China made handguard.  However, the handguard for the 9" 300 BO pistol looks a little nicer with at least a QD mount near the receiver.  Will look into MI handguards.

BTW, I would have possibly bought the 9" 300 BO pistol version as it was cheaper, however the twist rate is 1/5 which is supposedly causing issues with suppressors when used with supersonic ammo.  If a 300 BO rifle is not suited for use with supersonic, might as well go shorter if subsonic only.

I plan to remove the parts and put it on an SBR lower I have.  I was planning to use my Colt lower, however I notice the styling of the upper is a better match for my Quentin Defense Billet Lower that is also SBRd so unsure which one I will use.   The arm brace appears to use a buffer tube folder plus a regular AR15 sig arm brace.  I will remove the arm brace portion and use the folder mechanism with a regular AR 15 buffer tube and a stock.  I will take the left over arm brace and install it on the original Sig lower.

On a side note, the MCX Hybrid as sold has a LOP of 14.25".  So go figure, I thought that was an uncountable number and thou shall stop at 12.5"...

That has not been my experience after several hundred rounds of factory supersonic ammo.

I also received my "hybrid" 300 BLK pistol. F1 is at ATF now for long wait to take off brace and put on stock.  Can F4 sent as well, going with the Sig SRD QD can.

How do I tell if it's the updated charging handle, or not? I have a gen 1 post recall MCX, I guess I could compare the 2.

Received it the same day as I picked up a bunch of other freedom.

my pics didn't turn out as well as I had hoped, anyway:



fairly sure this is the old style charging handle








note the nut profile of the buffer tube hits the receiver before the brace, hoping a regular tube allows to bring the future mounted stock a little closer when mounted on SBR


for the first time I noticed the brace was canted, doesn't matter to me as I will part out the folder and brace and reattach the brace directly to the AR lower


inside view of the adapter


view of adapter from bottom


what does everyone think of the billet lower?  is it a better match from a styling point of view vs. using a colt lower?


other side of billet lower


would the upper function on a stock AR lower?  appears the AR lower would keep the spring assembly from flying out


6.75" Virtus Kit box and label


contents of kit

By the way, my hybrid charging handle is def different than my gen 1, so I guess it is the new one.

will your handguard accept a suppressor?  if I had to do it over again, I think I would have saved some a few bux and gotten the blackout pistol and then chopped the barrel to 8".

I just ordered one of these, I can't tell looking from the pictures if a Sig collapsible stock or SB brace will work with the M400 lower and adapter.

Anyone happen to know?

the MCX adapter has the rail to accept any of the MCX/MPX series of stocks.  You can remove the tube on the brace supplied with the pistol versions and use your own tube.  However the knuckle socket will swallow up more of the tube than a regular AR receiver so you may not automatically want to turn the tube into the knuckle as far as it goes.

I believe it's the same handguard as the gen 1 MCX..., NOT the virtus, so I don't think so.

That is an original MCX handguard, not suppressor width. So a can will not fit inside.

You would need a gen-1 MCX suppressor width handguard (NOT Virtus) purchased separately if you want your can to fit inside of it.

Or a Midwest Industries one.  They make handguards for both the Virtus and legacy MCX now.

There is the 8" MCX suppressor width handguard on sale at Sig Store for $50, however it is keymod.  I went ahead and ordered it anyway because for that price...  it will be for the 300 blackout setup.

the midwest industry handguards should have done better, at least based on the site specs, they show it 1.46" ID.  If they had just gone to 1.55" ID, it would probably have fit most cans people care about.   Instead they launched a seperate larger set of handguards that is probably overkill at 1.75" ID.

Anyone drop a Gearheadworks Mod 2, the new SBA3 Brace on a Hybrid Pistol yet?

Also, how is the OEM Flashider attached (Rocksett or Red Locktite)? I'm going to go with a SIG Q/D Can & I heard that they are a beeotch to get off.

Is there a way to use an aftermarket trigger besides the expensive Geissele MCX Trigger?

id like to know as well.. im about to purchase a hybrid pistol

Soaking and heat will be your allies in getting the OEM FH off.

You can use the dedicated Geissele MCX trigger or call SIG CS and you can get the “G” latch to use along with a “regular” Geissele trigger of your choice.

Please don’t attempt to shoot the upper on a standard M4-pattern lower without the adapter.

Is this a potential safety issue?

some newer pics although it now wears an MLOK handguard from Midwest along with an Aimpoint.







prior pics with MCX upper on AR lower with buffer tube was mock up only...