If you can not find data for a Remington unibody hull. You don't have a clue as to what you are trying to do.
I gave you a link to Hodgdon data. Use it. What powders can you find. Clays, clay Dot, American select, 700x, red dot, just to name few.
I could tell you 17.3 gr of clay Dot , claybuster wad cb1100-12, cheddite primer. But if you can not get clay Dot powder. What use is it.
Alliant has on line data also.
https://www.alliantpowder.com/reloaders/RecipeList.aspx?gauge=12>ypeid=3
Now if you say what powders you can find / have then someone can help. I load shotgun shells for myself and five others to shoot skeet, sporting clays , trap and 3Gun. It's not like loading center fire ammo.