I've done a boat load of reading lately about the dreaded "Marlin Jam". Everything I read has the jam occurring with the lever jammed open. I have recently been experiencing an intermittent jam on a JM 336 chambered in.35 Remington with the lever closed, locked up solid requiring a ton of force to open it up again. The rifle functions fine with Hornady Leverlution ammo but jams with Remington core-lok 200grn.
I have taken it apart, thoroughly cleaned and reassembled as well as made sure all screws are tight
Any suggestions would be greatly appreciated