Someone else, had the same exact problem.
https://www.thehighroad.org/index.php?threads/marlin-30-30-mod-336.868886/#post-11512555
Thx.
OCCAM’s razor — dried gunk.
Even though I soaked it overnight, soak it again.
Let’s suppose granddad’s gun sat in a closet for 30 years, and junior tried to shoot it, it wouldn’t shoot, so he traded it.
I will do solvent AND ultrasonic. Twice ;-)