In the 70´s when I reloaded for geese, I used plain wheat flour as a cushion filler with lead #BB.
The other components were Remington primer and case, a Winchester slow powder (#571???) and a Power Piston (yes, here in Mexico we only had Remington components, but now is worst, because we do not have any!!!)
1-1/2 oz of BB´s was 74 pellets and I put all of them in a 30 inches circle at 40 yds, the mitical 100% pattern with a full choke Mossberg shotgun.

All I said is because the flour works for tighten a pattern, very well indeed!!

Regards,

Jose

Jose M. Fernandez