Hornady still makes the Great Plains just not in the 58cal anymore.
With the roundball I shoot anywhere from 100gr - 125gr FFG. I like shooting balls more because they don't lead my bore.
Do you know how much those maxi-hunters you are using weigh?
The ones I shoot are casted. I got them from October Country and they weigh 615gr. I never played around with them too much but I suppose I should see if I can work up a load with them.
I also have a mold for some 58cal 440gr R.E.A.L's. I have not casted any yet but that reminds me I need to do so and try them out.
Kirk