yes. Now for some items I will outline below there is a big difference whether yo have the lower or not. ironically it is having the lower readily accusable to you within DC that limits you on certain items. This is due to "constructive possession" laws.
Examples:
Mags of 10 rounds or less. Looks like anyone can own them, receive them, possess them, transfer them registered gun or not. Does not even seem to be any laws for minor possessing them.
AR barrels. Same
AR upper: same
AR handguard: same
Examples of what you can have if you have no gun in DC, but cannot have if you do have a gun on which they fit in DC:
unapproved AR stock
AR barrel under 16"
rail mount forgrip
handgun Pistol barrel that has threads
Examples of what you need to have a DC registered gun to possess in DC:
Ammo, yes it is legal to ship to DC to a DC registered gun owner, just like NJ the owner emails a copy of relevant card.
What you can't have no matter, whether you own a gun or not, or have one accessible to you or not.:
- magazines over 10 rounds -- oh and it is a felony.
As far as I know there are no uppers that make an upper non compliant in DC, so unless there is one, you can ship to a gun owner or a non gun owner.