I picked up a Saint Victor .556 pistol. I want to replace the brace with one that’s adjustable.  I found one I like, the SB Tactical SBA4 Stabilizing Brace.

It says it’s for Mil-Spec Carbine extension platforms. The specs say it comes with a 7075 mil-spec receiver extension, and works with all platforms capable of accepting a mil-spec carbine length extension.

So I searched to see if the receiver extension on it was mil spec. I couldn’t find any info about it except what’s on Springfield’s site. So I emailed Springfield and asked if it would accept a mil spec carbine extension for an adjustable brace and said that it came with the extension.

The reply I got was...
‘That tube is not Mil Spec and will not accept an adjustable brace.‘

Ok...seemed like a strange reply. I just wanted to know if I am able to thread that mil spec extension into the receiver without issues. So I replied to that email saying...
‘I must have worded my question incorrectly. What I’m asking is if the receiver of the Saint Victor pistol is capable of using a mil-spec carbine length receiver extension? Also, is the stock receiver extension mil-spec or commercial?
Thank you!

Her reply was...
‘No it won’t!’

Another super friendly and helpful reply!

So I ended up calling their pistol tech, he said he’s not allowed to advise me on any modifications, but they have put adjustable braces on pistols.

So here I am, admitting I’m not very knowledgeable about the whole mil-spec/commercial receiver extension mess. Some things I’ve read say you can’t put a mil spec tube in a commercial receiver and other things I’ve read say you can.

Could someone with actual experience with this PLEASE shed some light on this for me? It seems simple, all I want to do is ditch the brace that’s on there and replace it with another. The problem lies in whether or not the Saint Victor can accept a mil spec carbine length extension tube.

Any help/advice is greatly appreciated

Mil-spec can mean many things with ARs, none of which are truly mil-spec.

“Milspec” in terms of marketing receiver extensions usually refers to the diameter, but can also refer to material or manufacture technique.

I looked at Springfields site, and none of the pistol I saw had an adjustable RE, like used with an SBA3 brace. They must be referring to material as “Milspec”, which is marketing hype.

You can install a Milspec  RE on a saint pistol.... it should be 4-position, forged 7075-T6 like found a Colt AR. That is the only commercially available AR that uses a true “Milspec” RE.

ETA: For clarification, the threaded portion of the RE is the same thread pitch.

https://www.ar15.com/forums/ar-15/buffer-tubes/128-723440/

Get your caliper out and measure the diameter. That should tell you. 1.14 = milspec 1.17 = commercial.

The Saint pistol, per SAI's website, uses the Trinity Force Breach Brace.  This brace, per Trinity Force's website, "is built to fit on all AR-15 pistol buffer tubes up to 1.25?".  My understanding is that a "pistol" buffer tube is simply round, without the bottom section that has the holes for an adjustable stock or brace to latch into.  So you wouldn't be able to just put an SBA4 on the Saint's tube.

However, the lower receiver on the pistol looks the same as the lower on the rifle, and the rifle comes with a BCM Gunfighter stock, which only fits a "milspec" carbine buffer.  So, in theory, there's no reason that you couldn't remove the pistol tube and install a milspec carbine tube for the SBA4.

Well there are three models of the Saint. The Saint is the base model that has the Trinity Force brace, then the Victor (the one I’ve got) which uses a SB Tactical SBX-K brace, then the top of the line is the Edge, and that one has an adjustable 4 position Maxim Defense CQB brace. In the specs for that is says the RE is Integral w/ Maxim System.

The brace I’m interested in comes with the compatible RE, that will function with the adjustable brace. It’s carbine length instead of pistol length. Which raises another question I had...do I need a different buffer and spring due to replacing a pistol RE with a carbine length?

I got out my calipers to measure but quickly noticed the RE on the pistol now gets thicker after an inch or so. It’s around 1.2”
I just found pistol buffer tubes on the SB Tactical website. The company that makes the brace that’s on my pistol now. And I’m almost positive I found the RE that’s on my pistol there. I’ll attach a photo. It does say OD of 1.2”

I’ll also attach a photo of the one I’d like to put on. It comes with (from the website)  ‘Product includes:  brace, 7075 mil-spec carbine receiver extension, adjustable nylon strap.’

And says is can be used on ‘all platforms capable of accepting a mil-spec carbine extension’

So do you guys see any issues with me swapping my pistol RE with this one? And would I need a new spring and buffer?

Thanks a million!

(I don’t know how to include images here. Looks like I’d need to have a link to image hosting)

No issue with swapping to the SBA4 extension. A standard  “pistol” RE is the same buffer and action spring as a standard carbine extension.

Things start getting weird with the PDW-Style braces like the Maxim. The SB-PDW uses standard  carbine buffer parts. However, if not most, use proprietary buffers and springs and in some cases even bolt carriers.

Great!!
I can’t thank you guys enough. I’ve spent a lot of time trying to get info about this. And just when I thought I had it figured out I got the reply email from Springfield telling me no I can’t do it.  So I really appreciate your help with this.

I just got a Saint Victor Pistol as well, and mine did not come with an adjustable brace.   However, I saw on the SA website, it shows the very same pistol as what you and I have, with an adjustable brace. In their specs sheet is says SBA3.