Im not at home but there are several decent loads using, 572, 20/28, unique and even herco.
Do be aware Remington 20s often measure 2 9/16 not the full 2 3/4. I trim them down to 2 1/2 with an exacting knife and a homemade chamber adapter that I just stick the hull into and trim off what sticks out above the top. I can still fold crimp them so super easy. I load them on a Spolar reloaded and it takes about five minutes to get my crimp fully adjusted.
Rem hull trimmed 2 1/2, unique 16.5, rem 209p primer, orange duster wad, 1155 FPS, 7.7kpsi. My shot bushing drops about five to seven pellets light with 7 1/2 shot so Im slightly under 7/8 ounce. With 9s its spot on. You could vary the load down to 15.5 grains for Summertime use and a bit lower pressures. When in doubt load up six and send them out for pressure testing.
Find a load close to what you want and modify to suit your needs. Then load six and get them tested. After that you have an nearly endless supply of safe reload, if you pick commonly available components. Known, verified pressures with decent velocity.
