With the release of the SBA3 brace, I finally decided to go the pistol route. I’ll just be using my AR M4E1 carbine lower with a BCM QRF 11.5 upper I just ordered. I mostly shoot my  AR at 100 M or less and live in an urban jungle , so everything about the move makes sense and should be fun
I plan on putting a vortex FH on it and swapping my BUIS and PRO from my DD 16” upper I currently use.

Stoked and thanks again to this forum for all the info

Sweet, post pics once you get it buttoned up.

I think you'll be pretty happy with the 11.5" - I know I love mine.  For me, it's a significant size difference from my primary 18" to be much more handy.  But it's enough length for decent midrange reach, especially with the right bullet selection.

With a 30-yard zero on my Red Dot, all of my shots are within 3" of the POA out to 250 yards.

The more I shoot my 10.5 inch 5.56 pistol the more I like it.  It's short, light, and pretty damn accurate even at 200 yds., perfect for HD/SHTF in my opinion.
My next build will be a 8-10.5 inch 9mm pistol.

A Vortex on an 11.5'' works very well. I have no visible flash during the daytime with the same set up.
I'm not sure if you know or not but you can not legally put a pistol length upper on a lower that started as a rifle/carbine. I think that is what your suggesting? If a lower started as a rifle or was first built into a rifle it must remain a rifle so adding a short barrel upper will create a short barrel rifle rather than a pistol even if the shoulder stock is removed. A PISTOL must start as a pistol and never have been a rifle.

Edit= With an 11.5'' upper you can reach 26'' or longer in over all length without an arm brace, (just a bare pistol or 6 position tube), I assume your lower has a 6 position tube. If you add a front grip to your 11.5'' upper it will be a ''firearm'' rather than a pistol when used with your lower. If you use a front grip you should be fine assuming the shoulder stock is removed.
If I misunderstood and your lower has never been used as a rifle then pay no attention to this.

I appreciate the replies. Honestly, I was scared to mess with anything pistol due to having to change out buffer parts AND the somewhat gray areas surrounding what is legal. the lower I am using is this a new aero precision M4E1 carbine lower, it came without a stock. So if i understand correctly, this is a NOGO UNLESS I use a VFG of some sort? Then I can slap an SBA3 on there and be good?

I thought the draw of this SBA3 was that you could truly put it on any lower and go. My lower does not specifically say pistol or carbine on it, just M4 and CAL MULTI as far as markings that might help

And  I just examined the PSA complete lowers with a brace, and those markings are the exact same as the regular lowers they sell. So does that mean they are wrong? Not trying to be a dick, just understand.

I am not expert, but if you used it as a rifle and bought it with a carbine tube with no stock, but never had it assembled with a pistol upper before that then it is pretty grey as in I doubt it is a good idea. Also if it came with a carbine RE but no stock the FFL may still have classified it as a rifle when you bought it.

this does open the question of whether you can buy a stockless Carbine tubed lower for pistol use?

Most lowers dont say rifle on them so that they can be used for either.

It was registered as other since it was not a complete rifle. Wonder if that changes anything?

My legal illiterate answer is if it was never assembled as a rifle, I cannot see the issue. but this is not legal advice, but I would probaby use it if it were mine.

this is unless someone with better knowledge on the issue shows the proper answer

Haha! I got you. I feel that is about as clean a slate as I could start with, so I will go ahead with that. I do appreciate the points you made and it makes sense. I doubt it would ever been necessary in any way, but I tend to worry about technicalities such as that so I would always try to cover my butt and do it as "right" as possible. Now I just need a brace

Have fun with your build! I completed my 11.5" BCM back in 11/2017. Currently in pistol form with the Kak brace until my Form 1 is approved.  I have the Trijicon MRO 2.0 on mine and hits the 16" gong at 200yds with ease. It's lightweight and compact, one of my favorite builds.

If your lower was transferred as an other then it can be built into whatever you want. The problem is, if the lower was built into a rifle first it can never be used as a pistol legally. A pistol must be ORIGINALLY designed or made as a pistol. A lower that was transferred as a rifle is obviously easy to track and determine it started as a rifle and can never be a pistol. A lower that was transferred as an ''other'' like yours must first be made into a pistol and then it can be switched from rifle to pistol and back as you please.  It must be a pistol first though!
At this point we will assume you have never used the lower as a rifle, if you had it could never be used as a pistol. Make sure you build a pistol first! Once you have built a pistol with your lower you can freely swap back and forth between pistol and rifle.
I know, it's dumb! Good to know the law in case you ever need to explain yourself though.

The VFG is a totally separate issue, and the markings on the lower are irrelevant to the matter at hand. He was just saying that if you're not using a "virgin" lower (specifically, a lower that has never been assembled with a stock to an upper), it could be issue. If you're starting with a lower that has never been assembled with a stock and attached to an upper, then you're fine. Even a complete lower that came with a stock would be fine as long as it was never assembled to an upper (and you removed the stock before assembling your pistol). When creating a pistol, the assembly history of the lower in question is paramount. The definition of a pistol requires that it was originally designed as a pistol; which is why starting with a lower that was first assembled as a rifle - by you or a factory - isn't acceptable.

Being able to utilize a VFG on a pistol/"firearm" build is another matter, and it relates to overall length. If the OAL of the weapon is 26" or more, you can attach a VFG to the weapon and its classification would then change from "pistol" to the plain ol' catch-all of "firearm". Otherwise, attaching a VFG to a pistol that is under 26" OAL would create an illegal AOW (NFA regulated) weapon. If you don't care to utilize a VFG on your build, you don't need to even worry about it.

ETA: Sneaky bastard posted while I was typing :\.

I finally get it. Thanks much. Yes, this lower will first be used as a pistol once my BCM upper and the SBA3 brace arrives next week. These laws are wild but I at least have enough of an understanding to get by without hurting myself too much. I will not be using a VFG either.

If this lower has never been built into anything, you do not need a vertical grip. The stupid ass rules say if you start as a pistol, you can go between pistol and rifle. If it started as a rifle, it cannot become a pistol.
With a brand new lower, you are good to go.
Good choice on the 11.5, I think it is the best length for a pistol.

Just FYI withe regular carbine RE and a 11.5" barrel, by my measuement it is long enough to use a VFG if you want to. I measured on mine a week or so ago.