For those reasons, I find that .45 Schofield/S&W is the answer. The case is smaller so there's less air gap, I want to believe the brass is a bit thinner and thus requires lower pressures to expand and fit to the chamber for full obturation, but in a .45 Colt revolver the .45 S&W is still capable of shooting the 250 grain bullets.
Howdy Again
Just for the fun of it I grabbed a handful of 45 Colt brass and 45 Schofield brass. They are all running the same thickness at the case mouth, right about .012 or .013.
I don't know about any other brands, but just about everything I load these days is Starline.
Regarding the case rim situation, standard rim diameter for 45 Colt is .512, standard rim diameter for 45 Schofield is .520. The only revolver that ever gave me trouble seating the larger rims of the Schofield rounds was an 'original model' Vaquero. As you can see in this photo, the area of the ratchet teeth on the Vaquero cylinder on the left has less clearance around the rims than the scallop shaped ratchet teeth of the Colt cylinder on the right. With that particular revolver, there was not quite clearance at one chamber only for the larger Schofield rims to seat all the way. About ten minutes with a file took care of the problem.
I don't think I have ever loaded 45 Schofield with Smokeless powder, I have only ever loaded it with Black Powder.
Here is an interesting photo. On the far left is one of my 45 Colt rounds, on the right is one of my 45 Schofield rounds. The 45 Colt round holds about 35 grains of Schuetzen FFg powder under the 250 grain bullet. (Modern solid head cases do not have as much case capacity as the old Balloon Head brass.) The Schofield round has about 28.5 grains of FFg Schuetzen under the 200 grain bullet. That 45 Colt round will do about 700 fps out of a 7 1/2" revolver barrel. Sorry, I have no velocity information for the Schofield round. The two funny copper cased rounds in the center of the photo are the original Benet primed, folded rim versions of these cartridges, 45 Colt on the left and 45 Schofield on the right. The odd crimps near the base hold the inside primed anvil plate in place.
Regarding why is 45 Schofield not as easily available as 45 Colt? I suspect it is simply lack of demand.