RE: pellets or powder
There are certain powders and powder forms which were designed for each other and work well together and certain ones that are very marginal; #11 and black powder will always work when used properly together, Musket caps and pyrodex will work well together; 777 loose FFF works but on an electric timer it has a delay that more or less impreceperable to humans 777 FF loose will work but some of use have had preceperable hang fires with it.
I have yet to see pellets work really well with out either a priming charge or using 209 primers or the 25apc type set up. Ignition is onethe reasons some people never get good groups, the other main one on sabot guns is not getting the right fit between sabot bullet and barrel. [ other than the ones that shake or wiggle while shooting]