A bit of a dilemma. I've never owned an inline myself, but I had a problem that was not at all unlike your own:
My flintlock loves a .530 ball and .020 patch. Shoots this load as accurate as I can shoot through the open sights--- all 5 shots inside a 4" bull. That's as good as I can see to shoot. I get 1820 fps out of my barrel, making my .54 flintlock the ballistic twin of a .44 magnum pistol inside 100 yards. The only problem is that this load requires a mallet to start! The short starter leaves a rather ugly looking dent on the face of the round ball, but this load is the most accurate, so apparently that doesn't affect things.
Now since I don't plan on carrying a mallet in my possibles bag while hunting, I load at the truck, and carry .018 patches for reloads. The .018 patches shoot
almost as accurate as the .020, and I'm able to start them without using a mallet.
Now, to apply this lesson to your situation, if you cannot make the load easier to load through the use of some lubricant, you may consider just living with it being hard to start, and find another sabot that shoots "close enough" to your current load, but loads easier, and use that load as back-up in the field.
But this is just free advice from a nutcase obsessed with goex and roundballs and flint. Probably worth what you paid for it.