If you were to make a launcher type upper that mounted an AR15 type lower, you'd need to register the lower as a Destructive Device correct? Think a modified can cannon upper that can retain munitions when pointed down and is capable of sending a bean bag round or rubber projectile(Anti-Personnel as defined by ATF).

Assuming so, if the Lower is registered as a Destructive Device could it also be temporarily configured into an SBR by swapping uppers so long as it was returned to it's DD configuration at the end of a range trip?

If not, can you double stamp a lower so that it could be used for either?

Thanks

No. Because the second you remove the portion making it a DD it no longer constitutes a DD.

I guess, would it be possible to register the upper receiver as the DD and the lower as the SBR?