Been there, done that. Winchester makes a superlight AA load, can't remember the name, but it is somewhere around 24-26 grams of shot and it travels at 980 fps. I have seen in print, but not personally tried, that this load will do fine in CAS.
For home loading of smokeless loads, I looked all over and finally found some 7/8 ounce loads at 1155fps. You can't duplicate the Winchester Featherlight(?) loads at home yet. Hodgdon publishes 7/8 ounce loads for WinAA cases and I thought that they worked well for me.
I am currently loading 7/8 ounce of shot in new paper hulls with black powder and a roll crimp. Graf and Sons has new Cheddite paper hulls, and I bought an assortment of old-fashioned wads from Precision Reloading and Ballistic Products. That, along with a shell vise and a roll-crimper. All works well with 2&1/4 drams, by weight, of 2F Black Powder and the 7/8 ounce of shot. All you have to do is use one nitro card wad over the powder and fill the rest of the column up so that it crimps properly. I use an 0.030" over-shot wad (this is old-timey wads, Not plastic). The drams of powder are drams Avoirdupois, which makes 2&1/4 drams about 61.5 grains. The Avoirdupois dram is not the same as the unit with the same name in Apothecary's system. That should be good for about 1145-1155 fps, but I haven't chronographed it yet.
The single drawback is that you must put some compression on the wad column to get uniform ballistics. I use a 650 MEC loader and put about 80 lbs of pressure on the wad column before I put in the shot. When I was a boy, in 1958, learning to load shotgun shells, we used old fashioned wads and tried very hard to get the right pressure on the wad column.
The old wads are only approximately the size that they are stated to be, as the material is not stable, dimension wise. Add to that you will have some compression of the powder and of the wads, making the pressure you put on the column change the column height. You gotta experiment with black powder to get everything to come up together at the right height. Nevertheless, it is possible to get some nice loads with a little experimentation.
Hop this helps