... and I believe at the time the form was marked rifle.
Several points about that.
1) The dealer screwed up, if that's what he put on the form. The instructions are clear about receivers and he should have known better.
2) This points out the absurdity of any sort of rule that tries to apply to what a gun once was, sometime. What matters here? IF the BATFE ever tried to enforce this, what would they go by? The dealer's 4473? Well, that was filled out in error. The manufacturer's records? Well, they shipped a bare receiver. That's what it WAS, when it arrived at the dealer's shop. But, of course, EVERY AR15 starts the same way. There is no difference at all -- not one atom's worth -- between a pistol receiver and a rifle receiver.
So, FIRST a rifle always a rifle? I'm still seeing two different answers.
Again, an absurdity of the way they say they want to try to enforce this. When you walked out of the dealer's shop it was (or should have been) an "other firearm." You then took it home and did WHAT with it? No one in the world could possibly say, definitively, except you. It probably is "covering your butt" to say you built it as a pistol first, but that's just your word against anyone else's word ... but NO ONE would have any better claim to make than you do, and you were there.
Especially considering that an AR15 "pistol" can be built with a rifle buffer tube, the difference is completely immaterial! Did you put your buffer tube on before you installed the stock? Of course you did. (You couldn't have done otherwise.) Then for a moment, at least, you'd constructed an "other firearm" at least, and maybe a handgun. (That would depend on whether the whole package was under or over 26".
I postulate that this is a completely unenforceable "rule" and they know it. They had to say
something but "awww, shucks, we can't possibly say one way or the other," just ins't something they can admit.
If I can't, then it's because a rifle can't be a pistol if the BATF determines it was first a rifle. Therefore all the rifle owners who convert their lowers to pistol configuration are doing so illegally.
Again, a distinction without any substance. The best that the BATFE could do is say that the manufacturer sold it as a complete rifle, and the dealer logged it as a rifle, so they have a case that it was FIRST a rifle.
Of course, we don't expect anyone to say they did.
And proving one way or the other would be practically impossible for either prosecution or defense.
As for the mag carrier, instead of a wrist brace a box magazine pouch installed on the buffer tube with a 20 rounder in it. It's not a shoulder stock, it's a spare mag carrier. It would be under the tube with the bottom of the mag toward the shoulder.
I haven't seen such a thing, but that's a mag carrier, not a stock.