Yes........ however if you have no s/n.............. and you didnt have to ncics it to purchase it...................
But..... If you read the ATF guide on what is a gun. You will see some possible problems that may or may not be dealt with later. The ATF says a gun is capable of firing a projectile by itself.
The uppers gained popularity due to the AR15 and the autosear. With this ability to self install an autosear, the ATF decided to classify the AR lower as the receiver. Odd since all the other guns they deal with the receiver is the receiver. But that worked out ok, since if you had an AR in 223 and wanted a 22-250, the swap was simple. the firing pin and hammer could be used from the AR so the barrel you received would not fire by itself, hence, not a firearm.
But then the 50 came on scene. Suddenly you need a barrel and bolt and firing pin, and hammer, and springs, ect. So if you put that 50 barrel down on a table, put a bullet into it, close the bolt, and hit the firing pin with a hammer, boom. Now since this scenrio shows that the 50 conversion can fire a bullet by itself, is it a firearm?
The upper manufacturers say no!! Its an upper!!!
But it does what ATF says a firearm must do to be a firearm. I asked an ATF agent out of curisoty one day and was told they were looking into that. But I have not asked since nor have I heard anything else on the subject.
To buy or not to buy? That is the question.
I chose the real gun, since I was not willing to chance some future ruling from ATF and their being able, if I was caught with it, to say I had a firearm that was not checked through NICS, and had no serial number, and I bought without an FFL. It just was not worth me being concerned about it.
Especially since the upper and all the hammers and springs and bipods, and tinkering with it and possibly have it beat my aluminum lower to pieces, cost about the same as several of the complete guns.
I even surmized that if I bought an upper and the ruling changed, I probally would not be caught with it in the first place. But my children reminded me that everyone in jail thought they would not be caught as well.
Anyway, uppers are legal to buy and own. At least today. Are they as good as a real gun? Don't really know, I can't do the time, so I spent an extra dime. I know my guns, even if outlawed, can be grandfathered in.
Eric