Well, to make a long story short, I gathered up a bunch shotguns and picked one to convert. I got interested in the bore guns, so I picked up a pair of Hastings 12 gauge rifled barrel blanks. Then I realized to make a DR using 12 gauge barrels, you need to make the rifle the old fashioned way...from scratch. Or as one very knowledgable member here said...get a 10 gauge shotgun and go the monoblock method.
The first thing I need to do is to taper the barrels to the same dimensions as the original shotgun barrels. The blanks are approx. 1.3" in diameter.