New Stock for P516

[masterdrago]

I want to change the SB15 on my P516 to a real stock like the Magpul UBR Collapsible Stock due to wanting to shoulder the weapon and because of the "cool factor".

https://www.magpul.com/products/ubr-collapsible-stock

Here is where it gets weird. The UBR comes with the necessary Entry-Length Receiver Extension tube. My question is will it fit on the receiver of the Sig.
An image of the RE is here...
http://i355.photobucket.com/albums/r...bum/Sig-RE.jpg

I measured the tube where the Brace slides on up to the hex shaped stop at a rather oversized 1.220". I measured the tube ahead of the hex near the Sig logo at 1.120". And the threads at 1.175". Certainly not a standard buffer tube.
I did take out the spring and buffer and they measure standard mil-spec carbine size.
If I get some other stock, what buffer tube would I need?
And yes, I've SBR form 1 the pistol. I did this because I did not want to be at the range, shoulder the SB15, and have a conflict with some officer of the law! Whole other can of worms.

[D_M]

When was your 516 manufactured?

[masterdrago]

D_M,
I got it from Able's Sporting in March of this year. They had just gotten it in and no other local gun shop had one. The buffer tube / RE is different than all of the others pictured on Sig web pages and their documentation that came with the P516. It may be some proprietary tube. The Brace can be taken off the tube with a bit of pressure. The total length is 7.25" and it appears to be an anti tilt design like at http://phase5wsi.com/hex-2-pistol-bu...x-2-clone.html

[masterdrago]

I guess what bothers me is that the dimensions on a mil-spec tube are different than the thread size of this one I have. I appreciate the help. It looks like with only (Sig RE 1.175") .010" difference from the Mil-spec or commercial, I can use either on because both will screw into the receiver. Just need the right stock for what ever tube I get. Is my thinking right on this? So that tube with the Magpul https://www.magpul.com/products/ubr-collapsible-stock has a mil-spec tube that will fit my receiver. The Magpul page does not indicate if 6061 or 7075.

[masterdrago]

Just got the born on date from Sig. Took about 60 seconds phone call. July 25th 2015

[GH41]

I have to ask.. Why on earth would you put a UBR on a SBR?

[masterdrago]

GH41,
I'm really new to the AR thing, so forgive me if that would be a major no-no. I just thought it looked really cool. Also, I want a real stock on the was pistol, now SBR. I also think adjustable would help my fit. I'm not a big guy so I could actually leave the Sig SB15 arm brace on and use it as a stock. I'm planning on adding some kind of optics later but 1st a stock. I'm really open to buttstock suggestions, so fire away.

Looks like the Gen II might work as well and is less $$$