I've been trying to solve this problem for awhile now.
It's a 1968 30/30 that looks to be in excellent condition. The primer is barely touched when it misfires. I tried some of these loads in a W94 and they went off.
A new factory main spring was put in. I cleaned the inside of the bolt by soaking in Hoppe #9, Than used a drill bit, bristle brush, and cloth till it came out clean. The firing pin and rear pin were polished. I swapped out an old 336 lever and tried to fire two duds. One went off the first time and the second took two hits before going off. I tried to smooth up any burrs that might impead the rear pin from going forward. I took the little spring on top of the rear pin completely out. The headspace must be ok. I put some dead primers part way in 3 cases, closed the bolt, and measured.
The firing pin protrudes plenty far enough. It does hang up a little bit when pushing it forward.
I figure it is the rear pin, firing pin or both. I don't want to buy parts if it doesn't help.
This has been posted on Marlin owners, and leverguns. Might as well try this forum.
I still get 2-4 misfires 8 or 10 good ones than misfires.
Does anyone have any suggestions. Thanks.