I am going to the range ASAP to find out the truth.
Whatever truth you discover will apply only to your rifle.
Bingo!!! I can only pass on what I have learned in over 30 years of hunting and shooting muzzleloaders...
Just like hand loading, you can have 2 identical rifles and have totally different results...
I would suggest swabbing the barrel between shots with 2 damp patches with rubbing alcohol on them, then a dry patch...
And try to seat each bullet with the same amount of pressure...
Start with one proven powder, like Pyrodex and one projectile...If I were to start with an Encore like you have, I'd go with a 250 Shockwave and 90-110grs of powder...
These things can show you a thing or two...I've seen something as small as changing sabots make a 2 inch difference in accuracy at 100 yards...
btw...Why do you specifically want to shoot a conical???