RE: Is it my shooting or something else?....
With shots that crappy (sorry), I would be looking beyond the black powder.
When I am using a scoped gun and my groups aren't even consistent, I start suspecting the scope rings. Are they properly tightened? Did you use loctite on the screws? Were you able to bore sight the scope?
I am not familiar with BP inlines, but part of your problem could be similarto a problem I had with a Ruger 17HMR-the receiver was way out of alignment. I should have figured that out when I couldn't bore sight the scope. It took a trip to Ruger repair to get it fixed (which they only got partially right)
Best of luck.