Kevin,
Are you shooting from a rest or offhand?
For load development, I would sure recommend a rest. And I like to do that at 25 yards, not 50. Once you get it tightened up at 25, then go out to 50 and see how it holds, says the person who hates to work on development.
Keep at it, and get some better patching, that you can't see through.
By the bye, how deep is the rifling?
John