AR and AK pistol receivers

[wabbit]

Hi everyone,
I tried searching for the answer to this question, but my search technique isn't up to par so I apologize if this has already been covered.

I have seen some AR-15 and AK-47 based pistols and got this weird idea of building up one from a bare receiver. They sell upper receiver kits for the AR pistol, but I noticed some fully assembled pistols are marked "Pistol" by the manufacturer.
1. Can I buy a bare receiver like the Smith and Wesson M&P15 receivers CDNN is selling and build it up into a pistol even though the receiver isn't marked "Pistol"?
2. I already have a Stag Arms AR-15 rifle, but I'm thinking it's not legal to use the receiver from a firearm recorded as being a rifle on a 4473 when I bought it to assemble a pistol. Right?
3. Are the laws regarding this as "once sold as a rifle, always a rifle" and "once sold as a pistol, always a pistol"?
Thanks.

[Diomed]

I speak of federal laws here, we can get into Virginia ones if needed.

1. Can I buy a bare receiver like the Smith and Wesson M&P15 receivers CDNN is selling and build it up into a pistol even though the receiver isn't marked "Pistol"?

How it's marked is irrelevant. What matters is whether the receiver has ever been assembled as a rifle, i.e., has it ever had a buttstock attached. So long as it has never had a stock attached, it can be built as a pistol.

Inquire with CDNN as to whether these are virgin receivers or if they've been stripped down from complete rifles. Usually new bare recievers are virgin but CDNN is a liquidator, so I suspect there's a chance they're stripped rifles.

2. I already have a Stag Arms AR-15 rifle, but I'm thinking it's not legal to use the receiver from a firearm recorded as being a rifle on a 4473 when I bought it to assemble a pistol. Right?

If it's a rifle, it can never become a pistol, legally speaking. You can make it a short-barreled rifle, or a weapon made from a rifle, but it cannot be a pistol.

3. Are the laws regarding this as "once sold as a rifle, always a rifle" and "once sold as a pistol, always a pistol"?

It's "once a rifle, always a rifle". A rifle is a rifle, forever and always. A pistol can become a rifle if a stock is attached, and it can never become a pistol again. (Certain exceptions exist for old firearms, but in general this holds.) While it doesn't matter how the firearm is sold - configuration and the history thereof are what matter - it's usually best to keep the paper trail consistent. A pistol is marked as such on the 4473, a rifle is marked as a rifle, and a receiver is recorded as a firearm (since it is not a pistol or a rifle).