I'll make a guess based on several older Marlins we've discussed on the Marlin Onwers site. The Hornaday Leverevolution ammo needs a different magazine follower that is dimpled, or you can drill a hole in the center of the follower, or the most simple fix is to alway load a conventional flat point bullet first, and then your new-fangled gummy tips.
Newer Marlins come with the modified follower. It can be purchased at many websites, such as Midway Arms. The gun should function normally with conventional flat point bullets.
Last edited by mogwai; 12/28/11.