45Hawken,
Why shouldn't you measure smokeless powder by volume? I reload standard cartridges and use a powder measure (volume) all the time, unless I'm going for extreme accuracy. When I measure by weight, I still start by volume, then check each load by weight/scales. It is only off by tenths of one grain.

I bet that if you would weigh your black powder charges, that you measured by volume, you would find that they are just as different.

I would go with the Savage simply for the ease of cleaning with the smokeless powder.

MH