the NFA rules were written along time ago, before the AR15 was invented, if you cut down a rifle to make a pistol that was easy to spot but an AR15 is different. How can they tell if you made an AR15 rifle and then put a pistol brace and short barrel on it at a latter date?
"How can they tell"
When you post about your intentions on a forum board that is probably monitored by the government. Like say INGO for example.
I'm not sure I completely understand your question.
An AR lower has the serial number. Let's call that the "serialized part." This serialized part of an AR was produced after the NFA and there is a record based on the serial number as to when it was produced.
Now, there's a form called the 4473. When a serialized part is purchased from an FFL, that's the form that details who the purchaser is and what category the serialized part falls into. That form will state whether the serialized part is for: a handgun, a long gun, or an other. If it was transferred as a long gun, then that's what it magically is. If they find a long gun serialized part with a shorter-than-it-should-be barrel, then there's an NFA problem. If it was transferred as a handgun or other, then it can be a handgun. Or it can be changed to a "rifle" as long as the shorter-than-it-should-be barrel isn't attached at the same time as the stock.
These are just observations as to what the current understanding is, not legal opinions or advice. There are many permutations and oddities, but that's the general idea.
Unless I misunderstood your question. Which is always possible.
"How can they tell"
When you post about your intentions on a forum board that is probably monitored by the government. Like say INGO for example.
okay it was legally registered on the 4473 as other does that make it a pistol or rifle. I think it comes down to what was on that 4473.
Once transfered as a rifle always a rifle.I've always been under the impression that "once a pistol always a pistol" but I could be wrong. Sounds like others have said as long as it's not registered as a pistol and you never assembled a SBR then it should be ok.
I purchased the stripped lower as "other" built the stripped lower as a rifle, now I want to build it as a pistol. The gun shop where I purchased the stripped lower says I can do it, are they correct?Once transfered as a rifle always a rifle.
if you assemble a kit from a stripped receiver, you can go from pistol to rifle; as long as the buttstock is nowhere near, or thinks about being near a sub 16" upper. If you BUY a pistol, you can change to a non NFA rifle, and go back to original pistol configuration at will. However, if you buy a rifle, it is always a rifle as swapping a short barrel onto it, by definition, is making a short barreled rifle.
if you build a pistol, then make it into a rifle, and sell it in rifle configuration it is now always a rifle. If you want to have fun, an AR pistol isn't allowed to have a vertical foregrip (it's a handgun, not hands gun) so you can build a "firearm" with an overall length (from crown of the muzzle, to end of the receiver extension (pistol buffer tube) greater than 26" and an arm brace, this firearm doesn't fall into any NFA definition, and you can use a vertical foregrip.
OP, the answer if it went thru NICS as a rifle, always a rifle. If you aren't sure, start with a $49 stripped lower (make sure it gets transferred as other, or whatever the third option is)and you're good to go
On the one hand we have a $49 lower.
On the other we have at least the 'possibility' of defending ourselves in court against a felony charge(whether successful or not almost doesn't matter when 'winning' will cost you some hundreds of times more than the lower). Losing of course will cost you all of that, plus your freedom and a lifetime of lost rights.
In what world does a multi-use lower balance against even the 'possibility' of legal trouble? If you want to build a rifle, buy a lower and build a rifle. If you later want to build a pistol, buy another lower and build a pistol. Continue doing this unimpeded for the rest of your life,......or take legal advice from LGS's and online gun forums. If you go straight to BATF for an answer you can rely on you will not get one.
Cheaper to just buy another lower I would think.