GutPile: Your right on with your comment. I also have a newer Omega Z5 with a Nikon 3x9 on it. I have tried loads with Pyrodex "P", "RS" Triple Seven FFg, and FFFg, Jim Shocky Gold "Crap", and 777 50 gr Pellets behind many different bullets. I found the 150 grain loads were less accurate off the bench with ALL bullets tested than was 130 gr of 777 FFg powder, behind the 295 gr powerbelt with a 777 primer. (Remington Standard 209 primers also worked well & Cheaper) The only problem was the powerbelts had a 3" group at 200 yds, but blew apart on deer closer than 150 yds. Yes they killed the deer, with a considerable amount of damage, but ruined a lot of meat! I know, shot placement has everything to do with it! But sometimes the perfect shot, doesn't go perfect! I ended up using The Hornady MAG Express sabots with a 250 gr jacketed bullet. WOW these are almost as accurate as the powerbelt bullet, (still working that load for more accuracy) but perform much better when they encounter venison!
Every rifle is different and working up loads is part of the experience with Black Powder hunting! Good Luck!