What I suspect is that you have a tight bore which is not uncommon. What makes your follow up loads difficult is the fouling buildup in the bore. This could be due to old pellets as GM-54 said or having some surface oil in the bore making the fouling adhere to it.
First thing I would do is to stop using the pellets and get some loose Pyrodex RS. If you were using 100 grain charge (2 pellets) start with 80 gr of loose. Next, make sure the bore is clean of all oils prior to the first shot. After the first shot swab the bore with a damp patch of black powder solvent (or even a spit patch) followed by a dry one. If your second loading or subsequent loadings are still to hard get yourself some Harvester Crush Rib sabots. For the Shockwaves you will need the black ones which are 50 cal for 45 cal bullets.
Honestly I think if I were you I would just go and get the Harvester sabots anyway and save yourself the headaches.
My Knight Disc Extreme has a super tight bore and I must use the crush ribs too.
Last edited by bronko22000; 09-23-2021 at 11:23 AM.