I cannot get myself to squeeze the trigger instead of jerking at it. I rest the gun, take aim and as soon as I'm on the target I'm lunging for the trigger and I cannot keep myself from doing it.
What load are you using? Maybe you are anticipating the recoil. Practice breathing control. Take aseveral deep breaths, let out half of the last one, hold itand just gradually squeeze the trigger.
Take a .22rifle to the range with you. After every couple of shots with the muzzleloader fire10-20 .22 rounds to steady things.