I have 2 of these "conversions" A thumhole stocked 22 hornet that was sleeved into 10" of 16 gauge barrel and receiver. It has folding leaf express sights and now a 6x scope. I can keep 5 under the inch at 75 yards no problem if I do my part.
The second was done on a cooey 12 gauge, same concept, bit more shotgun barrel. Took a barrel off a Win 94 with a busted tang on the receiver. put it in the lathe to fit the chamber of the shotgun and glassed it all in place with a couple of set screws. Awesome carbine, bit of recoild. has fibre optic Truglo sights on it. Both were registered with no questions - Cooey 840 calibre 30-30.