No. A jamb is the framework around a door. The "Marlin JAM" (as in traffic jam, not to be confused with PB&J sandwiches), is when a cartridge slips in under the carrier and locks itself between the action and mag... Lever is locked, can't move up or down... requires the removal of either the mag tube cap, spring & follower, possibly the lever & floorplate, or all the above. If not caused by a broken or badly worn carrier, it's caused by poor timing of the carrier, running the gun well outside the design limits. Pretty common in amongst cowboy action shooters & the mdl 1894 in .38/.357, although not limited to just the 1894.