I have come across this information whilst browsing a couple of times recently and thought it may be of interest.
The German and the British machine guns, being the same basic design, [from the Maxim] responded almost identically to defective ammunition, to wear and tear and to the failure of component parts.
Cartridges were fed, loaded, locked in place, fired and extracted somewhere between eight to ten times per second, and the lock had to withstand pressure between 45,000 and 55,000 pounds per square inch. The duty cycle of the complicated mechanism was quite heavy, and the moving parts and springs were prone to high rates of wear. In aerial use, the close- tolerance parts were subjected to the extreme cold of high altitude flying in winter; an environment for which the original design was not intended.
It was not uncommon for a fighter pilot, who had finally caught up with a high flying two-seater or airship, to have his machine guns fire just one round and then refuse to reload. The hump on the Sopwith Camel was actually a chamber which directed hot air from the engine onto the breech end of the guns to prevent that from happening.
The crank handles (or cocking handle/lever), which came in various shapes and sizes to suit aircraft types, made one backwards and forwards movement through an arc of about 110 degrees for each round fired. A jam would cause the handle to cease motion in one of four positions. The position in which the handle stopped was a reliable indicator of the basic type of jam which had occurred. Each position was known by a number, and machine-gun jams were described, for example, as ‘a number two stoppage’.
MAXIM-TYPE MACHINE-GUN STOPPAGE POSITIONS
A number 1 or 4 stoppage could be cleared in the air. The pilot would extract the defective cartridge by – pulling the crank handle back to the far stop and then releasing it. The spring return would feed the next cartridge into the firing chamber.
A number 2 stoppage caused by a tight cartridge case could often be cleared in the air. A small hammer, sometimes a wooden mallet, (secured by a strap) was carried in the cockpit, and the pilot would apply it vigorously to the crank arm to force it forwards to position 4. The expression: ‘the pilot hammered his machine gun’, means exactly that; not as portrayed in the movies as beating on the breech with clenched fists.
A number 2 stoppage, caused by the previous cartridge case having separated during extraction, would have the new cartridge telescoped into the broken piece. The crank arm. when hammered, would not move. To clear such a jam was a major operation that could only be performed on the ground. (No.2 becomes aptly named !)
A number 3 stoppage was generally impossible to clear in the air. Both a number 2 and number 3 stoppage could be caused by the pilot himself, usually a novice who had indulged in over-long bursts of fire. This overheated the breech mechanism thus destroying the lubricant and causing the delicate parts to seize.
A component failure, frozen moisture, dirt and/or congealed lubricant could also cause any one of the four types of stoppages.
http://ourairports.biz/?p=6277
Well, there it is, some, like me, may have found that of interest.. here's a LMG 08/15 in action where you can see the handle in operation: (shooting starts at 8min 30sec)
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