The Colt–Browning M1895, nicknamed "potato digger" because of its unusual operating mechanism, is an air-cooled, belt-fed, gas-operated machine gun that fires from a closed bolt with a cyclic rate of 450 rounds per minute. Based on a John Browning design dating to 1889, it was the first successful gas-operated machine gun to enter service.
An improved design based on Browning's prototype lever mechanism was offered to Colt by Browning in 1892. The lever was moved back, and power was supplied by a gas port about six inches (15 cm) back from the muzzle. To minimize heating during rapid fire, the gun used a very heavy straight contour barrel (finned for ventilation on later variants), bringing its weight up to 35 pounds (15.87 kg); the standard tripod mount with seat for the gunner added another 56 pounds (25.4 kg). Despite the heavy barrel, the closed bolt mechanism would cook off shots if a round was left chambered in a hot barrel. This required that the gun be unloaded immediately after an extended burst of firing. During testing of the gun, it was found to be capable of firing extended bursts of over 1,000 rounds before the barrel overheated and bullets began to tumble out of control; upon stopping, the red-hot barrel cooked off four or five additional shots before cooling down. The gun was originally chambered in 6mm Lee Navy and later, after the adoption of the Krag–Jørgensen rifle, in .30-40 Krag, 7×57mm Mauser caliber (the same cartridge used in the Spanish Model 1893 Mauser), and .30-06 Springfield in 1914. The 1914 version also included a lower tripod for firing prone; this is likely what led to the gun's nickname of "potato digger", as the operating lever would dig into the ground if it were fired from too low a position. The M1895 was made for export as well; the Russians ordered several thousand M1895 machine guns in 1914 in 7.62×54mmR caliber for use in World War I. In .303 British caliber, the M1895/14 saw service in England and France. The M1895 was also sold in 7×57mm Mauser caliber for use by various countries in South America. The Colt's unusual method of operation had both advantages and disadvantages compared to competing machine gun designs of the day. The lever-operated repeating action gave the weapon a relatively low rate of fire (less than 400 rounds a minute). However, the low rate of fire combined with a heavy barrel also allowed the gun to be air-cooled, resulting in a simpler, lighter, and more portable machine gun compared to water-cooled designs. Though combat reports of action stoppages were not uncommon, most of these could be overcome by manually cycling the action. As gunners gained experience with operating an air-cooled machine gun, it became apparent that avoiding long continuous periods of fire materially added to the weapon's reliability and barrel life.
Filed for patent in 1892, the M1895's operating mechanism was one of Browning's early patents for automatic rifles he had previously been working on lever action rifles for Winchester such as the Winchester 1886. The M1895 uses a unique operating mechanism, which is quite similar to that of a lever-action rifle. The earliest prototype developed by Browning in early 1889 was a .44 caliber black powder cartridge rifle, weighing under 12 pounds. Operation was via a rear-hinged lever located under the barrel, which operated the action when swung downwards and rearwards. The lever was actuated by the muzzle blast operating upon it. The bolt is a rear-locking tilting bolt, the first of its kind to be used on a machine-gun.