This query concerns whether a rifled 12 gauge slug shotgun can be loaded with black powder, to function like Victorian-era "bore" sized rifles. How much Swiss [brand] FFg powder - in weight in grains - can be put into the base 1.45 inches of primed unloaded new or once-fired, 12 gauge 2.75-inch high-brass shotshells? I specify Swiss black powder because it is denser than other black powder brands generally available. Being more dense might mean that more volume, and perhaps more weight, can be measured into the cylindrical shape. I'm not asking about any additional capacity that might occur by compressing the powder or using a drop tube. I just want to "get in the neighborhood." Other than high brass rather than trap/skeet shotshells, I'm not fixed on any particular brand or other specifics.