Fledwell: I assume you're using a pretty light load? Back when God and I were a lot younger, I read of folks using oatmeal on top of the powder, in very light loads, with the bullet compressing everything to prevent mixing.
For the hell of it, one time, I used my 200-gr SWC .45ACP load of 5.8 gr of 231, but in my .44 Mag with 255-gr bullets. Lots of empty case, there. I noticed no "irregularity". If it's the powder which might make a difference, maybe, alternatively, a Bullseye light load? It's easily ignited, which might make the difference if you don't like the oatmeal idea.
Gun-tilt of muzzle-up or -down makes a group-size difference in a Garand, too, with GI ammo. It's nothing new...
Best regards and good luck.