Another 12ga sabot idea, first picture is a 570 gr USS slug, with Powder Cup seal from BPI, locked to USS discarding sabot section. This shortens column so that we can get more of the slower powders in we use, in shorter 2.75" cases. With slower powders, they get to peak pressure a little easier so that the cushion usually between seal and sabot/slugs isn't needed. This locked on seal will aid in smoothbore accuracy and it will work of course in rifled barrels. This sabot has a peg on the back that locks it in original setup to the green USS cushion base/seal, and we just pried it apart and drilled tight hole to match in the Powder Cup seal, and forced it on for a locked fit.. Slug is .629" diameter.
Next picture is 3 sizes of first USS sabot slugs, with the locked on bases which work good with them. Giving nearly rifle accurracy in smooth bores.
Here is older picture of couple of Rodda 4 bores. Man what nice old guns.
Next picture is a 1.5" Minie ball slug, might work for close to a one gauge. It is next to older 37mm case which might fire it also. Maybe a way to make a one gauge of sorts, if.......I get enough ambition...Ed