They would ber deigned with the inside tapered plastic walls - WW hulls, I would think.

I'd resort to normal loading practises by that, I mean if one accesses a loading manual and begins loading with reduced loads and works towards velocity and patterning results, about any hull should be useable. Note, that the wads designed for tapered wall hulls might allow powder to move forward in non-tapered hulls. A simple thin overshot wad will not take up much space, will allow the plastic cupped base of the wad to do it's job in sealing powder gasses behind the wad and will hold the powder under the wad, which is the main use.

Always start at the bottom again, when changing any component, from the primer up to the type or style of crimp. The slower burning powders give much more leeway (safety) in shotshell loading, as long as there is room for them. Very ligth loads with slow powders can result in bloopers, but these are not dangerous as they are in rifles as detonation doesn't seem to happen in shotshells - perhaps due to the relative ease of moving shot loads through a smooth bore. ALWAYS take a cleaning rod with you to the range when testing shotloads - handy for clearing wads that stick in the bore form bloopers. Slow powders sometimes have a narrow window where they work properly. If you can get 7625 or 4756, that's where I'd start as most 1 1/4oz 1,300fps loads with them produce only 8,000 to 8,500CUP IIRC.