building an AR pistol... does the lower have to say "pistol only?"

[Nwcid]

So if you wanted to carry in the car and then shoot some PDs while out,you could have a 20" upper/barrel on your pistol lower.Or just carry the spare with you.
And not have a butt stock in the vehicle.(?)

Yes you could have any size upper and you could have a stock on it or with you. You can legally put a 16"+ barrel and stock on a pistol no problem. Legally you can not change it back to a pistol configuration according to the ATF (in the case of the AR). There is a specific exemption for the Thompson Contender which should apply to all guns but the ATF has said it only applies to the TC and no one has fought it yet.

But if you DID do such a thing,it would be wise to have the lower marked "pistol" to show the LEO it was in fact a pistol
And not have a butt stock in the vehicle.(?)

Well if you feel better about stamping "pistol" on your gun sure go for it. It MIGHT make an LEO feel better but simply stamping "pistol" on something has no bearing on its legal status. I could stamp "pistol" on a stick but it is still just a stick......

IF your AR pistol is built right it will have a buffer tube that will not readily accept a stock (to be legal) so having a stock (unless some how it fits on) would not be a problem. Do you worry about having a stock in your car while you carry any other pistol?

Man a guy should have a folder in his car with the laws to show the LEO if you're gunna carry a AR pistol around

Somedays it feels like that.

 

[motoman98]

It's defined in a backwards manner,as is usual in the law. A barrel for a rifle must be at least 16 inches in length: less than that is a pistol. Exception is the sbr rules and license requirement. Illegal to turn a rifle into a pistol, but not to turn a pistol into a rifle. Once a rifle, always a rifle though.