What shape is the bullet "Oddball/SWC/IDP#1/grooveless, Missouri sells them all in 200gr?
I will bet the OAL is too long.
Remove the barrel from the gun, put a bullet in the chamber, it'll stop when it hits the rifling, slightly oval a fired case and push it into the chamber over the bullet until the case mouth touches the step in the chamber.

Carefully push the bullet/case assembly out from the muzzle.

Carefully measure the assembly without pushing the bullet deeper in to the case.
This measurement is the longest OAL for this bullet and should be at least 0.010 shorter when loaded.
If you don't mind pulling bullets you can assemble dummy rounds (no primer no powder) with 0.010 shorter increments of OAL, and try them in the barrel chamber (not the gage) until short enough to seat.
Also check a round that "got caught up in the barrel" for marks on the bullet where it jammed into the rifling.
good luck,