So, I’m sitting around recovering from pneumonia when I see that Sig made an adapter that will let you attach one of the MCX retractable (HK style) stocks to a 556/556xi. Does anybody know where these can be found or if they are still available? I have 2 early 556 and 1 xi sbr’s and I’d love to outfit them with these. Thanks.

This part? http://www.sigsauerguns.com/si...-adapter-x-fold.html

Probably this part http://www.sigsauerguns.com/si...er-psb-1913-blk.html

Pretty cool - Didn't know they made this. Currently out of stock at Osage though....Might be available elsewhere

The one I saw was just a Pic rail (like on the MCX receiver) so you could attach the stock of your choosing (I prefer the HK style to the M4 tube). When I did a search one popped up in a picture that had Osage’s logo, but I couldn’t find it on their site. This is gonna drive me nuts.

While they do offer that stock adapter, I’m curious whether the HK style retractable stock would work on the 556s. Both the MCX and MPX receivers have grooves in the sides for the stock rods when it’s retracted. The 556s don’t.

Here you go....

From the CDNN Website:

SIG SAUER PSB STOCK ADAPTER PIC RAIL XI 556/552

Manufacturer: SIG SAUER
Model: 556XI
SKU: SIGADAPTERPSB1913BLK
UPC: 798681530243
In Stock: 99 units

Regular Price: $88.00
Special Sale: $29.99

https://www.cdnnsports.com/sig...52.html#.Wt39qbjMj5w

That’s the one! 2 on their way. Thanks guys!! CDNN was probably the only place I hadn’t checked.

nice find! My google-fu didn't come through because I left the dashes in. I'm gonna order a few too because I like the idea of running a modern stock on my 553's

quote:

Originally posted by nhracecraft:
Here you go....

From the CDNN Website:

SIG SAUER PSB STOCK ADAPTER PIC RAIL XI 556/552

Manufacturer: SIG SAUER
Model: 556XI
SKU: SIGADAPTERPSB1913BLK
UPC: 798681530243
In Stock: 99 units

Regular Price: $88.00
Special Sale: $29.99

https://www.cdnnsports.com/sig...52.html#.Wt39qbjMj5w

I don't see any latch mechanism on this adapter. What keeps the stock from inadvertently swinging closed from the open position?

quote:

Originally posted by Modern Day Savage:

I don't see any latch mechanism on this adapter. What keeps the stock from inadvertently swinging closed from the open position?

It doesn't fold. The folding mechanism of a normal 556 stock is the hinge pin and push button in the stock itself. This adapter goes in one side with that little nub and then the pin holds the other side in. Any folding mechanism therefore must be present in the MCX stock itself or the folding adapter to buffer tub (which is a Rube Goldberg-esque combination of parts but guess it would work).

quote:

Originally posted by nhracecraft:
Here you go....

From the CDNN Website:

SIG SAUER PSB STOCK ADAPTER PIC RAIL XI 556/552

Manufacturer: SIG SAUER
Model: 556XI
SKU: SIGADAPTERPSB1913BLK
UPC: 798681530243
In Stock: 99 units

Regular Price: $88.00
Special Sale: $29.99

https://www.cdnnsports.com/sig...52.html#.Wt39qbjMj5w

So will that adapter make this stock fit my 556Xi lower?

quote:

Originally posted by PGT:

quote:

Originally posted by Modern Day Savage:

I don't see any latch mechanism on this adapter. What keeps the stock from inadvertently swinging closed from the open position?

It doesn't fold. The folding mechanism of a normal 556 stock is the hinge pin and push button in the stock itself. This adapter goes in one side with that little nub and then the pin holds the other side in. Any folding mechanism therefore must be present in the MCX stock itself or the folding adapter to buffer tub (which is a Rube Goldberg-esque combination of parts but guess it would work).

Ahhh, ok. I'm familiar with the SAN SIG 55X/ 556 folding mechanism. So, if I understand your explanation correctly, this adapter's lug locks into the recess at the back (left) of the 55X receiver and, essentially it simply replaces the typical push-button locking mechanism with a fixed locked adapter not designed to fold, but the attached PSB or stock would include a folding or telescoping mechanism?

I've handled/ examined a SIG MPX and MCX, but I didn't spend much time examining the stock mounting points.

So, I was thinking that this adapter was also used for the MCX/ MPX. I guess my next question is, do all MCX/ MPX come from the factory with the vertical picatinny rail section fixed to the back of the receiver, or are there some variants that would require this 55X adapter to mount a stock?

What's your OAL with the stock collapsed on the bottom picture?

Thanks bigarms for starting the thread and to everyone that contributed!
DWD1985, that looks great and perfect for my needs ... Thanks too for the heads up with the stock lengths, I'm looking forward to getting the same parts!

I've been Struggling with the stock on my P556-SBR ever since I replaced the rail with the one from MFI that has the integral Swiss type rear sight at the back. For the primary sight I have a ACOG 4x NSN that (that I've had forever)the sight fits perfectly under the eyepiece and you can still use the irons with it mounted, however now the ACOG sits further forward on the rail and with the fixed length stock it's difficult to get a sight picture ... I also like that it will make the whole package thinner.

I'll post pictures when everything arrives!

Well the plate got here Monday and the stock on Tuesday, put it on last night and took it to the range this afternoon. It must have been the tornado watch because there was no one there!


Sorry about the crappy lighting. I realize it was actually a few inches shorter with the folding stock but with the retractable stock it's about half the width of the folded stock ... It's just over 24" with my QD mount.



It now fits in my oldest case, originally bought for an UZI ... The folding stock made it too wide to zip up completely, but not now!
Oh, the stock, when it's fully extended is about 1.25" shorter than the fixed folder and as I'd hoped, it's just right for me to get the proper eye relieve now that the scope has to set further forward with the MFI sight-rail installed.

Sharp looking there kimberkid. That’s what I was hoping for. I got my mounts, just need to pick up a couple of stocks now.

what's the SKU on the stock?

quote:

Originally posted by PGT:
what's the SKU on the stock?

SKU 11172591 is what it was on GunBroker, Wholesale Hunter was who I bought it from, $174.96 was the best price I could find at the time

quote:

Originally posted by kimberkid:
Well the plate got here Monday and the stock on Tuesday, put it on last night and took it to the range this afternoon. It must have been the tornado watch because there was no one there!


Sorry about the crappy lighting. I realize it was actually a few inches shorter with the folding stock but with the retractable stock it's about half the width of the folded stock ... It's just over 24" with my QD mount.



It now fits in my oldest case, originally bought for an UZI ... The folding stock made it too wide to zip up completely, but not now!
Oh, the stock, when it's fully extended is about 1.25" shorter than the fixed folder and as I'd hoped, it's just right for me to get the proper eye relieve now that the scope has to set further forward with the MFI sight-rail installed.

That really looks great. I ordered an adapter. Can the cocking handle cycle fully rearward on the 556 with the stock in the closed position?

Josh, I didn't try that on Wednesday but last night I put a SWAT hand-guard on it and had it in the back of the truck to run out to the farm on my lunch hour ... it I had to trim the MFI rail because it was too long to fit the rail of the SWAT handguard and still just touches ... I wanted to see if/how much it would effect the trajectory with a cold and hot barrel.

So, in answer to your question ...

With the stock collapsed, the charge handle will go back far enough to cock the hammer and just back far enough to strip a round off the mag. There is about .5" that the stock tube covers of the charge handle slot.

The stock tubes have three lock cut-outs, one being fully collapsed, the second about 3/4 full open and then fully extended. I unlocked it from being fully retracted, took a shot and the handle pushed the stock back a couple inches ... so it definitely hits the tube when fully collapsed, which kinda bums me out. Although I'm not the guy that blasts from the hip either.

A bit better? picture


Josh, or anyone else! Do you know of an available gas valve designed for a suppressed setting? I have one for my 553 but would really like to have one for my 556.