He bought a new 45/70---- and it will not feed the Hornady 325 Grain !! Have a look and see where it might be catching . Then ask where you got the gun or better still phone Marlin , before you do anthing to the gun. After you have tinkered with it, Marlin may afterwards not want to fix it .
The company ( Marlin ) seems to be quite good @ service , so give them a chance .