A lower is a lower regardless of what the engraving says, the only markings that matter are the ones that are required for an SBR. There was debate about this and the caliber markings for quite some time but as long as you meet the criteria for making an SBR your good to go
I understand that as far as SBRs are concerned, a lower is a lower. Perhaps I need to ask the question better... Legally, an AR lower is a firearm, hence why they must be bought through an FFL. ARs can come in two flavors: pistols and rifles. You can make an SBR by adding a stock to the pistol or by reducing the barrel length on a rifle and I get that to make an SBR, the ATF doesn't care whether you're slapping a stock onto a pistol or shortening the barrel on a rifle. Rifle or pistol, that lower is now registered as an SBR (yes, not technically an SBR until the hardware is added/removed/changed, but you have the ATF's permission to make the SBR applied for in the Form 1).
Let's not even talk about NFA for a second... For lowers sold as pistol lowers, wouldn't they be treated just like any other pistol and lowers sold as rifle lowers be treated just like every other rifle? Granted a lower is a lower from a practical standpoint, but in the ATF's eyes, wouldn't an AR pistol lower be sold, bought, and fall under the same laws and regulations as all other pistols and a rifle lower be sold, bought, and fall under the same laws and regulations as all other rifles?
Or do lower receivers fall into their own classification until stocks and barrels are added to them? In particular, I am talking about stripped lower receivers.
I guess the question does not even have to involve SBRs. The question is whether the stripped lower receivers that I'm talking about need to be treated as pistols if the pistol lowers are bought and treated as rifles if the rifle lowers are bought. For instance, I recall hearing that one can make a pistol into a rifle, but cannot make a rifle into a pistol unless that rifle started life as a pistol. Therefore, it would make more sense to buy the pistol lower and have the flexibility to go back and forth between rifle and pistol if I should choose. On the other hand, pistols tend to be more regulated and have different, usually slightly more restrictive laws concerning their purchase, sale, and use.
Thanks for the replies. It is confusing. I hope my question makes sense. Thanks!