Yes - there is a definite possibility of the "other" barrels 'projectile' to move off the powder- especially if it is a bullet rather than a patched ball.
I used patched balls only in mine and likely why I got it to regulate. I have heard of these guns diverging (shooting apart) by over a foot at
50yards, if shooting slugs in them. Converging is shooting towards each other, then crossing, diverging is shooting apart. The more recoil, the
& lower velocity, more they usually diverge.
Here is a group at 50yards, rest with my rife with the load that shot both barrels together.
Only one sight was used & held identically for each shot.
IIRC, there 8 shots in that group, including the 'slight' flinch or bad hold, one or the other.
The main 7shot group is about 1 1/2" or a little less.