Friend storage of SBR length AR upper only question...

I would like to know if my friend can legally store his soon to be purchased 11.5" bbl'ed AR upper receiver w/BCG
in my safe, at my home, along side my registered AR SBR?
He does not wish to violate Fed law by purchasing and storing the SBR length upper along side his standard bbl length
ARs. Just not sure of the legality of this.
Please help...Thanks, member Tom S. in TX.

Very likely not a problem at all. Always think of the three C's when determining possession: care, custody and control. If you do not have all of them, you do not have possession. IANAL...