No paradox, but did develop RB loads for a 12 bore SxS with "FLUID STEEL" barrels. I'm assuming it was an early 1900's, export shotgun from the UK. I cut the tubes to 24 or 25" IIRC. The original chokes were .705", or improved modified. The bores were .724" - a "tight" 12.
I used BP as well as smokeless and found smokeless loads with 7625, 4756 and blue dot (no longer have the data) that shot a .682" round ball, held in the centre of the bore with the cut-off base of a WAA12 white trap shot cup. I used another one, cup-down on the power with whatever fiber cushion wads in between for the correct wad height to get a star crimp.
I was pushing the balls with smokeless, at the same speed (1,500fps) as the 7 dram black powder load I finalized with. The BP load of 191gr. was really hard to shoot in the light 12 bore, but the smokeless loads also shot to the "sights" I installed on the 'raised' rib.
The velocity was roughly the same as I got in my .69 cal. ML, using a mere 6 drams with a tightly patched round ball.
Accuracy wise, I could plant a right and a left on a 10" square piece of steel at 100 meters, shooting offhand. I had mounted a scope on the gun for load testing. It worked very well.
Shot only one deer with it, at about 100yards. The ball hit the deer, must have been on an exhale, between the spine and the lungs, making a visible hole, both sides.
I lost that deer and actually searched for it, for 3 FULL days. I'm sure I walked past it's dead body at some point, maybe, but could not find it. I am or was a good tracker, yet could not find the deer. There was no blood trail at all. It should have been an easy kill, but I guess, just too long a distance. sickened me to lose the deer and I did not hunt the rest of the fall. This was mid October and no snow.
Oh, further note, with the BP load, I learned to put a hard card on the BLACK powder, as if a plastic wad is on the power, the bore will be coated with melted plastic. Had to use a tornado brush (spooled stainless) to get it out.
Oh, further, the first shot I took with the BP load, split the stock which I had to repair before further testing.
From W.W.Greener's book, there were 3 BP loads listed, 110gr.= 4 drams, 150gr. = 5 1/2 drams and 191gr. = 7 drams.
I sold or traded the gun to my buddy Keith, who sold it to a friend of his, who used it for grouse and moose.