I was pondering this the other day... 922(r) applies to assembling firearms that would be restricted from importation, and those are, of course, those that are determined to not be "particularly suitable for, or readily adaptable for sporting purposes". Nothing new for most guns, of course - make sure your parts count is good an keep moving.
However, the verbage that allows shotguns w/ a bore over .5" is pretty much the same. Any gun w/ a bore over .5" is a DD, "other than a shotgun or a shotgun shell which the Secretary finds is generally recognized as particularly suitable for sporting purposes". So.... if a shotgun w/ a bore over .5" is determined to not be importable in a certain configuration (because it is found to be "non-sporting"), would that not make it a DD by default in that configuration, regardless of parts count?
I know that SG's have only been named DD's by make/model so far, but I believe that was because the AWB enacted shortly thereafter made anything similiar illegal anyway. Since it looks like the AWB will indeed sunset, I expect this to come up again - as people start their conversions and the antis try to grab at whatever remaining they can.
Rocko