The Marlin Model 120 Magnum is a 12-gauge pump-action shotgun manufactured between 1971 and 1985 (with some sources indicating 1974-1975 for specific Magnum variants) in North Haven, Connecticut, designed as an affordable, steel-receiver alternative to the Winchester Model 12. The shotgun is known for its heavy-duty construction, walnut stocks, and available 38- to 40-inch "Goose Gun" barrels. JM stamped.