TMP .357 PISTOL: Includes: - (1) US made .40 cal mag - 3-Piece Rail Kit w/Hand Stop -2 position marked lower * This unit runs a Micheals Machines Tungsten filled .40cal/.357/10mm Bolt Carrier & comes with 1 US made .40 cal Magazine .357 Tri-Lug and Threaded Barrel with thread protector Heavier .357 Recoil Spring. Uses Standard .40cal UMP Magazines. ** If caliber change is desired, this unit is compatible with .40cal and 10mm Barrel's