The barrel is surrounded only with the standard version with a perforated casing to improve the cooling. In contrast to M2, the HB version (English heavy barrel = heavy barrel ) for a longer run. 50 caliber machine gun during a Pre-aimed Calibration Fire (PACFIRE) exercise. The new machine gun was first manufactured in 1921, several revisions and incorporated in 1933 in its final version. Only after a German Anti-tank rifle ( was captured tank gun model 18 ) with ammunition in caliber 13 mm, it became possible to develop a service with sufficient ammunition to penetrate the armor then usual. The first tests in October 1918 did not show all the desired results - in particular the bullet velocity was too low and difficult to control the weapon - were still 10,000 units of the model Browning M1918 (.30-06 caliber, appointed with water ) from the U.S. 30 in a stronger version of the cartridge. According to some sources, Browning and Winchester are already at that time such a weapon of similar design have worked, as the official order was issued, but it was still here at the caliber. The French munitions but was deemed too inefficient, it was John Moses Browning with the development of a very heavy machine-gun charge, the Winchester Repeating Arms Company (New Haven, Connecticut) should develop the appropriate ammunition for it. Army in France, became aware of French 11 -mm ammunition, which was used by the French against armored targets and reconnaissance balloons. This should change when Colonel John Parker, an officer of the MG school of the U.S. You needed to defend themselves against armored vehicles, but had not the appropriate weapons for it. The gun went from the experiences of U.S.