I have the ballistic products buckshot manual, but it's at work. I'll take a pic of the 20 gauge pages on Monday if I can remember. All their loads are listed by weight, not by a specific size pellet or count. The buckshot loads in other manuals are anemic.

Ive found several good buckshot loads for 12 and 16 gauge. The best patterning loads I have found for both stacked by 2s in a wad. I use Longshot in my 12 gauge loads and Blue dot in my 16 load.

I roll crimp all mine, it will give you extra room in the hull. Just make sure the slightly longer shell will cycle in your gun.

I would bet money you could find a 12 pellet #1 load that will do good. A typical #1 pellet weighs 40gr x 12 is 480 grains. 480 ÷ 437 = 1.09 oz. That would be safe to use in a 1 1/8 oz load