Sig MPX sbr

Hawkeye · Feb 23, 2016

Speed3 said:
I'm interested in option 2 Alex lol

From some quick reading, it might be on the "silly" end of things - I've seen one spec that the OAL with the telescoping stock is right around 24". That would mean 5" of padding added to the telescoping stock, which..... eeeehhh... I don't know about that.

smdub · Feb 23, 2016

Picked up today. Some measurements for everyone:
MPX-C w/ orig 3/8" buttstock adapter = 32.5" (manual says there is a 1" one avail to adjust LOP and would obviously add 5/8". I can't find one for sale though. Same one the MCX folder uses.)
Barrel measured w/ a wood dowel down the bbl w/ the bolt closed (method ATF uses) = 16-3/16"
The factory bbl sticks out 2-3/8" past the carbine handguard.
So you could lop off 3.5" of bbl = 12-11/16" bbl for a SBR if you don't pin anything on.

I've already ordered parts for the stock to make it longer :cool:

Thinking outloud: Assuming the 8" pistol barrel is actually 8" (and not slightly longer/shorter) Hawkeye is right: You'll need almost 5" to reach the MD 29" limit.

Hawkeye · Feb 23, 2016

smdub said:
I've already ordered parts for the stock to make it longer

What are you going to use, and how much longer are you going for?

I've thought about a bunch of options for one:

Buying a carbine and cutting the barrel.
Buying a pistol and just leaving the SIG Brace on it.
Doing either of the above and then making what I really want if either a) Engage wins their lawsuit, or b) the Kolbe case is concluded and we win.

schnejerator · Feb 25, 2016

OK, for those of you going the AR receiver extension path...

Poor photoshop hack job and actual details about getting to 29" aside, MFT BMS (top) or Magpul SL (bottom)?

Any other options that look halfway decent on this piece? Picking up pistol tomorrow, very curious to see what wait times on Form 1 do in the next several months...

Flipz · Feb 25, 2016

Just got my form1 approval back for my Gen2 MPX a couple weeks ago. Today I got my lower back from engraving and put everything together. I used the side folding adapter (X-Fold) that came on my MPX with the arm brace. The folding adapter, 6 position buffer tube, and CTR stock with extended buttpad got me 29.2".

Speed3 · Feb 26, 2016

Flipz said:
Just got my form1 approval back for my Gen2 MPX a couple weeks ago. Today I got my lower back from engraving and put everything together. I used the side folding adapter (X-Fold) that came on my MPX with the arm brace. The folding adapter, 6 position buffer tube, and CTR stock with extended buttpad got me 29.2".

Nice, but how are you going to run a suppressor is its a folding stock?

smdub · Feb 26, 2016

He doesn't believe a suppressor is a flash hider per MD law. (He and I have had this argument in person many times

)

smdub · Feb 28, 2016

Note: These pics are all taken on my MPX *CARBINE*. I do not own a MPX pistol, so I don't have any problems doing this w/o an approved SBR stamp.

Collapsed, the stock is 8" from the 'flat' of the picatinny rail to the end of the stock. Thats about 3/8" shorter than the original stock fully extended. Yields about 12" LOP. Extended, it is a little over 13.25" & 17" LOP. Several of my friends have MPX pistols and they tell me the OAL is 16-1/16" (with the flash hider removed) but I have not confirmed this. That would add up to 29-3/8 if you put this on an SBR approved pistol

FWIW, It currently only has lock positions at both ends. One could be added in the middle to any desired LOP.

FWIW: This is just 'version 1'. I can make the stock collapse 2" shorter but I ran into several tooling problems. A new collet I have is ground the wrong size :mad54:

and I can't find another end mill I thought I had

. Will have to order both to proceed with version 2.

Hawkeye · Feb 29, 2016

That is totally genius, and I love it. Two inches shorter when collapsed would be icing on the cake. Where would you gain that from? It doesn't look like the bars can slide any further forward on the receiver, because they're at the end of the cutouts.

Could you conceivably make these for others?

I need to go get my stupid HQL so I can buy the pistol.

Speed3 · Feb 29, 2016

Hawkeye said:
That is totally genius, and I love it. Two inches shorter when collapsed would be icing on the cake. Where would you gain that from? It doesn't look like the bars can slide any further forward on the receiver, because they're at the end of the cutouts.

Could you conceivably make these for others?

I need to go get my stupid HQL so I can buy the pistol.

Where can I get one of these?

Hawkeye · Feb 29, 2016

What one of these are you referring to?

If you mean the stock in the video above, that's something that smdub is working on building, so nowhere, yet.

If you mean the MPX, they're all over the place. I know that Free State in White Marsh had several of the pistols the last time I was in there a few weeks ago - one with no stock, and one with a folding SIG brace. I know that other IPs here regularly carry them also.

smdub · Feb 29, 2016

Hawkeye said:
That is totally genius, and I love it. Two inches shorter when collapsed would be icing on the cake. Where would you gain that from? It doesn't look like the bars can slide any further forward on the receiver, because they're at the end of the cutouts.

Correct, the bars can't slide any further forward. Patience Daniel-san

Its going to be quite a bit more machining work and time is money.

Could you conceivably make these for others?

Yes.

I need to go get my stupid HQL so I can buy the pistol.

Or buy the carbine, get SBR stamp, and chop and thread the barrel. I have my HQL but still went that route because the carbine already comes w/ the hard-to-find stock and the long handguard (which isn't avail YET separately from Sig. Knowing them it won't be avail for years. :rolleyes:

) Plus the rifle is cash-n-carry so you can buy or transfer though a VA IP and pickup the $60-ish mag at the same time. Disadvantage of that route is you can't run a suppressor on the carbine unless you SBR it. The flash hider is pinned on (~14" bbl + 2" flash hider)

Not sure what Sig was thinking about when they did this.

Hawkeye · Feb 29, 2016

smdub said:
Correct, the bars can't slide any further forward. Patience Daniel-san Its going to be quite a bit more machining work and time is money.

Oh, sure, get me all excited and then tell me to wait...

Yes.

Awesome. I want one.

Or buy the carbine, get SBR stamp, and chop and thread the barrel. I have my HQL but still went that route because the carbine already comes w/ the hard-to-find stock and the long handguard (which isn't avail YET separately from Sig. Knowing them it won't be avail for years.) Plus the rifle is cash-n-carry so you can buy or transfer though a VA IP and pickup the $60-ish mag at the same time. Disadvantage of that route is you can't run a suppressor on the carbine unless you SBR it. The flash hider is pinned on (~14" bbl + 2" flash hider) Not sure what Sig was thinking about when they did this.

Yeah, I've run the thought process on this a bunch of times. I've decided I really want an MPX. I'll likely have to sell some stuff to do it, so I want to make sure I do it "right." My ideal endpoint is an SBR with the collapsible wire stock on which I can run a suppressor.

Your wire stock will allow me to run the 8" barrel version. To get there, I could do pistol, or carbine with cut barrel, or carbine and later install a pistol barrel.

I need to do a little more reading, because I'm under the impression that the gas port and system are slightly different between the pistol and carbine barrels, and with the shortened dwell time on a cut barrel it might act oddly if you cut it.

So that leaves either a) buying a pistol or b) buying a carbine and later on buying a pistol barrel. That would also mean the expense (and maybe impossibility, given SIGs record with parts...) of buying a pistol barrel.

With all of that, plus that if I ever want to shoot it unsuppressed, I will want the shorter handguard anyways so I'm leaning pistol.

But your point about the carbine being cash and carry and coming with the stock is a good one...

Blah.

schnejerator · Mar 1, 2016

Awesome, smdub!

dc44 · Mar 2, 2016

I'm still trying to figure out how to get something like what the MPX-C would have been before the lawsuit, even if you need a stamp or two to get there. I've found a couple of rail dovetail adapters that would let you mount a buffer tube without the folding mechanism, which will decrease length a bit compared to those linked above but would then permit flash hiders. The descriptions call them "pistol" adapters, but the ID threads are the same for all AR-15 buffer tubes or we'd need pistol/milspec/commercial lowers.

http://www.kakindustry.com/mpx/mpx-adapter
http://www.amazon.com/Sig-Sauer-Mpx-Stock-Adapter/dp/B013M20LHO

The Innovative Arms integral suppressor barrel looks promising to add some more length (essentially a permanently affixed shroud with removable monocore baffles) but exact sizing is hard to come by online.

https://www.youtube.com/watch?v=qRqzo7graMc
http://innovativearms.com/portfolio/smpx-sig-mpx-integral/

Gambler · Mar 3, 2016

dc44 said:
I'm still trying to figure out how to get something like what the MPX-C would have been before the lawsuit, even if you need a stamp or two to get there.

Agreed, they should just sell the barrel they made with the suppressor. I'd buy it in a heartbeat. It would only be one stamp that way to boot.

Hawkeye · Mar 3, 2016

I just found another collapsing option.

No idea about OAL or anything like that, and not sure that I love the way that it looks, but it's a choice:

http://www.safetyharborfirearms.com/products/kes-kompact-entry-stock/product/70-kes-mpx

Mike OTDP · Mar 3, 2016

Gambler said:
Agreed, they should just sell the barrel they made with the suppressor. I'd buy it in a heartbeat. It would only be one stamp that way to boot.

This. I'd buy one. I think SIG missed an opportunity there.

CATMdude · Mar 3, 2016

smdub said:
Note: These pics are all taken on my MPX *CARBINE*. I do not own a MPX pistol, so I don't have any problems doing this w/o an approved SBR stamp.

Collapsed, the stock is 8" from the 'flat' of the picatinny rail to the end of the stock. Thats about 3/8" shorter than the original stock fully extended. Yields about 12" LOP. Extended, it is a little over 13.25" & 17" LOP. Several of my friends have MPX pistols and they tell me the OAL is 16-1/16" (with the flash hider removed) but I have not confirmed this. That would add up to 29-3/8 if you put this on an SBR approved pistol FWIW, It currently only has lock positions at both ends. One could be added in the middle to any desired LOP.

FWIW: This is just 'version 1'. I can make the stock collapse 2" shorter but I ran into several tooling problems. A new collet I have is ground the wrong size and I can't find another end mill I thought I had. Will have to order both to proceed with version 2.

I'd love one of these! I have a pistol, I've been waiting to SBR hoping a non-AR stock way of getting to 29" would come around!

fireman5980 · Mar 5, 2016

Another option

Here is another option. I'm talking with the guy now about making longer rails.
It's already almost 2" longer extended than standard factory stock.

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Sig MPX sbr

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