Pistol upper legal to own?

[SDW]

I am considering getting a pistol upper to add to the pile as well.
...
As I stated earlier I will just build one of those with a brace, buy the pistol upper and take a few pictures to avoid any gray areas.

Again, no such thing as a "pistol upper". It's just an upper with a short barrel (by legal def, under 16"). Especially if it's something that's just to "add to the pile"---of other uppers presumably. May as well start using the correct terminology at this point of the thread.