Recoil operation is an operating mechanism used to implement locked-breech autoloading firearms. Recoil operated firearms use the energy of recoil to cycle the action, as opposed to gas operation or blowback operation using the pressure of the propellant gas.
History The earliest mention of recoil used to assist the loading of firearms is sometimes claimed to be in 1663 when an Englishman called Palmer proposed to employ either it or gases tapped along a barrel to do so. However no one has been able to verify this claim in recent times, although there is another automatic gun that dates from the same year, but its type and method of operation are unknown. Recoil-operation, if it was invented in 1663, would then lie dormant until the 19th century, when a number of inventors started to patent designs featuring recoil operation; this was due to the fact that the integrated disposable cartridge (both bullet and propellant in one easily interchangeable unit) made these designs viable. The earliest mention of recoil operation in the British patent literature is a patent by Joseph Whitworth filed in 1855 which proposed to use recoil to partially open the breech of a rifle, the breech then being manually pulled the rest of the way back by hand. Around this time, an American by the name of Regulus Pilon is sometimes stated to have patented in Britain a gun that used a limited form of recoil operation. He had three British patents related to firearms around the 1850s to the 1860s; however, all of them refer to a means of dampening recoil in firearms, which wasn't a new idea at the time, rather than true recoil operation. The next to mention recoil operation in the British patent literature is by Alexander Blakely in 1862, who clearly describes using the recoil of a fired cannon to open the breech. In 1864 after the Second Schleswig War, Denmark started a program intended to develop a gun that used the recoil of a fired shot to reload the firearm, though a working model would not be produced until 1888. Later in the 1870s, a Swedish captain called D. H. Friberg patented a design which introduced both flapper-locking and the fully automatic recoil operated machine gun. Furthermore, in 1875 a means of cocking a rifle through recoil was patented by a German called Otto Emmerich. Finally came Hiram Maxim's 1883 fully automatic recoil operated "Maxim gun", which introduced the modern age of automatic machine guns.
Design
The same forces that cause the ejecta of a firearm (the projectile(s), propellant gas, wad, sabot, etc.) to move down the barrel also cause all or a portion of the firearm to move in the opposite direction. The result is required by the conservation of momentum such that the ejecta momentum and recoiling momentum are equal. These momenta are calculated by:
Ejecta mass × ejecta velocity = recoiling mass × recoil velocity The barrel is a moving part of the action in recoil-operated firearms. In non-recoil-operated firearms, it is generally the entire firearm that recoils. However, in recoil-operated firearms, only a portion of the firearm recoils while inertia holds another portion motionless relative to a mass such as the ground, a ship's gun mount, or a human holding the firearm. The moving and the motionless masses are coupled by a spring that absorbs the recoil energy as it is compressed by the movement and then expands providing energy for the rest of the operating cycle. Since there is a minimum momentum required to operate a recoil-operated firearm's action, the cartridge must generate sufficient recoil to provide that momentum. Therefore, recoil-operated firearms work best with a cartridge that yields a momentum approximately equal to that for which the mechanism was optimized. For example, the M1911 design with factory springs is optimized for a 230-grain (15 g) bullet at factory velocity. Changes in caliber or drastic changes in bullet weight and/or velocity require modifications to spring weight or slide mass to compensate. Similarly the use of blank ammunition will typically cause the mechanism not to work correctly, unless a device is fitted to boost the recoil.
Categories Recoil-operated designs are broadly categorized by how the parts move under recoil.
Long recoil
Long recoil operation is found primarily in shotguns, particularly ones based on John Browning's Auto-5 action. In 1885 a locked breech, long recoil action was patented by the Britons Schlund and Arthur. In a long recoil action, the barrel and bolt remain locked together during recoil, compressing the recoil springs. Following this rearward movement, the bolt locks to the rear and the barrel is forced forward by its spring. The bolt is held in position until the barrel returns completely forward during which time the spent cartridge has been extracted and ejected, and a new shell has been positioned from the magazine. The bolt is released and forced closed by its recoil spring, chambering a fresh round. The long recoil system was invented in the late 19th century and dominated the automatic shotgun market for more than half that century before it was supplanted by new gas-operated designs. While Browning halted production of the Auto-5 design in 1999, Franchi still makes a long-recoil–operated shotgun line, the AL-48, which shares both the original Browning action design, and the "humpbacked" appearance of the original Auto-5. Other weapons based on the Browning system were the Remington Model 8 semi-automatic rifle (1906), the Remington Model 11 & "The Sportsman" model (a model 11 with only a two-shell magazine) shotguns, the Frommer Stop line of pistols (1907), and the Chauchat automatic rifle (1915).
Cycle diagram explanation Ready to fire position. Bolt is locked to barrel, both are fully forward. Recoil of firing forces bolt and barrel fully to the rear, compressing the return springs for both. Bolt is held to rear, while barrel unlocks and returns to battery under spring force. Fired round is ejected. Bolt returns under spring force, loads new round. Barrel locks in place as it returns to battery.
Short recoil
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