APEX Gun Parts is your source for hard to find gun parts, parts kits, and accessories. We specialize in all military surplus weapons from AK-47s, AR-15s, Mausers, CETME, Enfields, UZIs, and much more We set ourselves apart by supplying unique parts at a good value and standing by our products by offering outstanding customer service. M2 4.2-inch Mortar specification CreatorUser United States of America Denomination M2 4.2-inch Mortar Caliber 107 mm Effective firing range 515 m Maximum firing range 4,023 m Rate. Anyone know how to date a 2 inch mortar. I know Bren guns have the date stamped on them or Stens have serial numbers. Although my mortar has a serial number, is there reference to serial numbers and dates or would a proof stamp have a date Register; Forgotten Your Password Remember Me Knowledge Library. MKL Entry of the Month;. The M2 4.2 inch Mortar was a heavy mortar used by the United States during World War II. The M2 could fire 107 (4.2 inch) mm rounds at a maximum range of 4,200 m. Unusual to most others, the barrel of the M2 was rifled, removing the need to have stabilizing fins on the mortar rounds. Because the mortar was often assigned to chemical mortar units, the M2 was also often given.