Editing Vickers machine gun (section)

==Operating mechanism==
[[Image:VickersMuzzleBoosterAnim.GIF|right|thumb|Animation of the Vickers muzzle booster operation, showing the expanding gases pushing the barrel to the rear relative to the cooling jacket|200px]]

The Vickers is a fully automatic [[Belt (firearms)|belt-fed]] firearm which is fired from a [[closed bolt]].  When ready to fire, a [[Cartridge (firearms)|round]] is in the [[Chamber (firearms)|chamber]] and the [[breechblock]] assembly and working parts are forward.  It has a [[Recoil operation|recoil operated]], [[floating action (firearms)|floating action]] with a toggle lock similar to a [[Luger pistol]].  However, unlike the Luger, the mechanism is totally contained within the receiver or body of the Vickers. When operated, the floating action, which consists of the barrel, breechblock assembly and toggle mechanism, reciprocate as a unit within the body of the gun.  The mechanism is held together by recoiling plates, that connect the breech end of the barrel to the rear of the toggle mechanism. The breech is locked closed when the toggle is straight. The [[Crank (mechanism)|crank]] cocking handle is part of the floating action.  It acts through the rear pivot of the toggle lock.  Pulling the cocking handle causes the toggle to rise.  This unlocks the breech and then draws the breechblock assembly rearward.  While firing, the opposite end of the crank handle cams on a round lug fixed to the body.  Rearward movement of the floating action tips the cocking handle and unlocks the toggle.  The recoil that unlocks the toggle is [[Muzzle booster|gas assisted]].  Propellent gases leaving the muzzle are partly contained within the muzzle cap and act on the muzzle cup (attached to the barrel) to assist in propelling the floating action rearward to the point where the toggle mechanism is unlocked.  The breechblock assembly then opens fully while opposed by a spring which ultimately returns it to the closed position.  The spring under tension acts on a crank mounted on the opposite side of the body to the cocking handle.<ref name="vmg opp 1">[https://www.youtube.com/watch?v=26U1eguqg1g TAB Episode 52: Vickers Gun Disassembly], accessed 14 July 2021.</ref><ref name="vmg opp 2">[https://www.youtube.com/watch?v=gG2YfcAJrtU&t=3s Vickers Mk1 1914], accessed 14 July 2021.</ref><ref name="vmg opp 3">[https://www.youtube.com/watch?v=7eYJXNXzqCk&t=1116s Vickers MG study: H 5529 (and the Vickers machine gun mechanism)], accessed 4 July 2021.</ref>

The feed block assembly sits directly above the breech.  It accepts the canvas belt loaded with ammunition.  With each firing cycle, it advances the belt by one round so that a fresh cartridge is presented ready for loading.  The belt is advanced by [[pawl]]s which move from side to side.  The pawls are operated by a linkage that engages with the floating action.  A second set of spring-loaded pawls tilt up and down as the belt passes over them.  These hold the belt during the return cycle of the feed pawls.<ref name="vmg opp 1"/><ref name="vmg opp 2"/><ref name="vmg opp 3"/>

The breechblock assembly is roughly as high as the receiver of the gun. On its front face is the extractor block.  Levers cause this to move up and down as the action is cycled.  It has a slot with two grooves which allow the [[Rim (firearms)|rim]] of the cartridge to be held from each side, much like a [[stripper clip]] does.  With the breechblock assembly closed and ready to fire, the extractor block grips the base of two cartridges: the lower cartridge in the chamber ready to fire and an upper cartridge held in the canvas belt within the feed block.  When the breechblock assembly unlocks after firing, the extractor pulls the spent cartridge from the chamber and, once clear, this falls through an ejection port in the underside of the gun's body.  Unlocking the breechblock assembly also withdraws the upper round (the next round to be chambered) from the belt.  When there is sufficient clearance, the extractor block lowers the new round until it is aligned with the chamber.  Forward movement of the breechblock assembly then chambers the round.  Near the very end of the forward cycle, the extractor block rises to engage the next round ready to be loaded.<ref name="vmg opp 1"/><ref name="vmg opp 2"/><ref name="vmg opp 3"/>

The breechblock assembly houses the [[firing pin]] and [[Trigger (firearms)|trigger]] mechanism.  The firing pin, under spring tension, strikes the [[Centerfire ammunition#primer|primer]] of the cartridge through a hole in the extractor block.  It must therefore be retracted before the extractor block moves down as part of the loading cycle.  Once retracted, the firing pin is held in a cocked position by a [[Sear (firearm)|sear]], ready for the next firing cycle. As the breechblock assembly fully closes on the breech, the sear disengages but the firing pin is held rearward by the trigger.  The end of the trigger protrudes from the top of the breechblock assembly.<ref name="vmg opp 1"/><ref name="vmg opp 2"/><ref name="vmg opp 3"/>

To fire the loaded gun, the gunner depresses a paddle at the rear of the gun. Through a lever, this pulls on a sliding bar that trips the trigger to release the firing pin.  The weapon then cycles to load the next cartridge for firing.  If the paddle is still depressed when the breech closes, the trigger is tripped again and a further firing cycle occurs.<ref name="vmg opp 1"/><ref name="vmg opp 2"/><ref name="vmg opp 3"/>