It is not always better to add more powder just because you can. It is my experience from shooting the MH that you get your best accuracy/velocity/consitancy in the 85 to 95 grain by weight range. Don't load by volume!

You can change things a bit by using different brands and granulations of black powder. But loads in the 85-95 grain range will leave air space in those big cases. Air space is not good. So you have to add something to take up the space.

Load up enough powder so you don't have an airspace and can compress doesn't improve things. Recoil becomes unmanagable because of gun design and accuracy falls off.

So all that's left is fillers. Check the LoC and you will find fillers used. We are not talking foil cases here, we are talking drawn cases.

The folks here convinced me to use more filler and compress that for better results and I did and it works. I did ignore part of their advice, I use Kapok instead of dacron.