Sig Brace Question / Advice

[MMA10mm]

I know this is going to be speculative but I'm asking for input before proceeding:

I'm thinking about sling options for my AR-Pistol (w/ SigBrace). I'm wanting the rear sling-attachment point near the end of the SigBrace. I have been pondering attaching the sling to the web strap, but this seems pretty unstable as the tension could pull the web strap off the rear end of the SigBrace while it's hanging from the shoulder, and there is no good way to stop the sling from sliding vertically along the webbing, both of which are less than ideal.

First, I thought about drilling a hole in the SigBrace in order to attach a sling swivel at a fixed point. (I'd use a fender washer and a dome-headed bolt, so one's arm can still pass through the tunnel and use the SigBrace as a stabilizing pistol brace, as designed.) Then I wondered why I couldn't just drill and trim a slot in the SigBrace in order to loop the sling around the brace itself so the strap passes through the rear 1.5" of the tunnel and then out a slot (I would cut) and then run under the SigBrace's web-strap. Again, doesn't change the designed use of the Sig-Brace, as one's arm just slides along the short bit of sling strap which is inside the tunnel, leaving the designed purpose fully capable.

Then, while I'm at it, I'm thinking it would be nice to put a blind pin through the receiver extension and SigBrace so that it will not rotate and resist sliding off the rear of the receiver extension...

So, as I'm pondering my wonderful ideas, I remember a caution I read somewhere that one should be extraordinarily careful about modifying the SigBrace so as not to violate the FTB letter's intent.

My thought is that neither of the modifications I am pondering would prevent the SigBrace from being used as designed, nor change it to a rifle:
- The pin actually makes the SigBrace more stable as a pistol-brace. In fact, stopping the SigBrace from rotating or sliding makes it a BETTER pistol arm-brace.
- The sling loop (swivel or hole idea) does not prevent one from sliding their arm through the SigBrace, and as long as the person attaches their sling properly (under the SigBrace's original tightening strap), it does not prevent the SigBrace from being used as a pistol arm-stabilizing brace. (One's arm just slides along the sling through the tunnel of the SigBrace, and the tightening strap will still tighten the SigBrace around the forearm.)

So, I'd like you guys' to give me any Devil's Advocate arguments you can think of. In addition, and perhaps my paranoia is getting the better of me, but do you think a letter from the ATF is needed to get their opinion on these modifications?

[rjacobs]

I wouldnt think pinning through the buffer would work due to the whole reciprocating assembly inside. Maybe if you did it really far to the rear or possibly somewhere else where you wouldnt interfere with the buffer and spring or you used a REALLY short pin that only went through the brace and wall of the extension without interfering with the buffer and spring.

[MMA10mm]

I wouldnt think pinning through the buffer would work due to the whole reciprocating assembly inside. Maybe if you did it really far to the rear or possibly somewhere else where you wouldnt interfere with the buffer and spring or you used a REALLY short pin that only went through the brace and wall of the extension without interfering with the buffer and spring.

Sorry, I neglected to mention that I am using a KAK Industries extended tube. About the rear 1.75" of it is solid, and that's where I was think of doing the pin. On reflection, I'm still deliberating about this. A pin through rubber would probably wallow-out the hole in the rubber. May have to modify this concept as well... Still, the question stands about BATFE getting upset about modifications...?

[Randygmn]

Don't do it. If I recall correctly, part of the brace being approved is that it is held on ONLY by friction. A pin alters COMPLETELY how it is affixed to the BT.

[tfbit]

I wish KAK would machine a QD socket into the end of their tube, like Spike's Tactical does, but they seemed to have no interest when I asked them about it. It might be pretty easy to bore a small hole in the end of the KAK tube and press something like this into it:

http://www.gearsector.com/view/product/164/description/

[Mako181]

If you have the KAK Tube drill/tap a hole in the back to attach a sling swivel. You have solid metal at the end that will allow this so would be the best bet in the way you would like your sling. That or a different end plate such as one like this from MidSouth:

https://www.midsouthshooterssupply.com/ ... ick_Detach_