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A breechblock (or breech block) is the part of the
firearm action of a typical double-barreled shotgun, with the action open and the extractor visible. The opening lever and the safety catch can also be clearly seen. In firearms A firearm is any type of gun designed to be readily carried and used by an indi ...
that closes the breech of a weapon (whether
small arms A firearm is any type of gun designed to be readily carried and used by an individual. The term is legally defined further in different countries (see #Legal_definitions, Legal definitions). The first firearms originated in 10th-century Histor ...
or
artillery Artillery is a class of heavy military ranged weapons built to launch Ammunition, munitions far beyond the range and power of infantry firearms. Early artillery development focused on the ability to breach defensive walls and fortifications dur ...

artillery
) at the moment of firing.


Variants

A way of closing the breech or chamber is an essential part of any
breech-loading weapon A breechloader is a firearm A firearm is any type of gun A gun is a ranged weapon designed to use a shooting tube ( gun barrel) to launch typically solid projectiles, but can also project pressurized liquid (e.g. water guns/ cannon ...
or
firearm A firearm is any type of gun A gun is a ranged weapon designed to use a shooting tube ( gun barrel) to launch typically solid projectiles, but can also project pressurized liquid (e.g. water guns/ cannons, spray guns for painting ...
. Perhaps the simplest way of achieving this is a
break-action Break action is a type of firearm action of a typical double-barreled shotgun, with the action open and the extractor visible. The opening lever and the safety catch can also be clearly seen. In firearms A firearm is any type of gun designe ...
, in which the
barrel A barrel or cask is a hollow cylindrical A cylinder (from ) has traditionally been a Solid geometry, three-dimensional solid, one of the most basic of curvilinear geometric shapes. Geometrically, it can be considered as a Prism (geometry), ...
, forestock and breech pivot on a hinge that joins the front assembly to the rear of the firearm, incorporating the rear of the breech, the
butt Butt may refer to: * Figurative or literal ''blunt ends'': ** Butt joint A butt joint is a technique in which two pieces of material are joined by simply placing their ends together without any special shaping. The name 'butt joint' comes from t ...
and usually, the trigger mechanism. A breechblock is a separate component and is not a feature of the break-action. A breechblock must close against the breech for firing but be able to be retracted or otherwise moved for loading or unloading or to remove a spent
cartridge Cartridge may refer to: Media * Broadcast cartridge, used in radio stations * 8-track tape cartridge, a 1960s-1980s music storage format * Compact Cassette, used with sound recording and reproduction and data storage for early microcomputers * ...
. This article primarily addresses the matter of breechblock design, as opposed to the
action ACTION is a bus operator in , Australia owned by the . History On 19 July 1926, the commenced operating public bus services between Eastlake (now ) in the south and in the north. The service was first known as Canberra City Omnibus Se ...
, which relates more with how the mechanism is operated, even if the distinction is not always clear.


Rotating bolt

Usually referred to as a bolt rather than a breechblock, a
rotating bolt Rotating bolt is a method of locking the breech (or rear barrel) of a firearm closed for firing. Johann Nicolaus von Dreyse developed the first rotating bolt firearm, the "Dreyse needle gun The Dreyse needle-gun (German ''Zündnadelgewehr'' ...

rotating bolt
is perhaps the most common variant. It is so called, because its operation is similar to a pad bolt or barrel bolt. The bolt slides in the receiver along the axis of the barrel and is rotated in the same axis to lock or unlock it against a closed breech. It is the basis for the
bolt action Bolt action is a type of manual firearm action of a typical double-barreled shotgun, with the action open and the extractor visible. The opening lever and the safety catch can also be clearly seen. In firearms A firearm is any type of gu ...
, in which the bolt is rotated and retracted by an handle attached to the bolt. In some designs, the handle (sometimes called a
cocking handle The cocking handle, also known as charging handle or bolt handle, is a device on a firearm which, when manipulated, results in the bolt (firearms), bolt being pulled to the rear, putting the hammer (firearms), hammer/firing pin, striker into a sprin ...
) rotates to lock against a shoulder in the receiver or body of the firearm. This type of locking is usually reserved for low-pressure applications such as the .22 cal rimfire series. More often, the bolt locks closed with two or more lugs that operate like a
bayonet mount A bayonet mount (mainly as a method of mechanical attachment, as for fitting a lens to a camera using an matching Lens mount) or bayonet connector (for electrical use) is a fastening mechanism consisting of a cylindrical male side with one o ...

bayonet mount
. Multiple lugs permit a smaller degree of rotation to lock and unlock the breech. Most types are front-locking and have the lugs mounted near the breech face. A notable exception is the rear-locking system used in the
Lee–Enfield The Lee–Enfield is a bolt-action Bolt action is a type of manual that is operated by directly manipulating the via a , which is most commonly placed on the right-hand side of the weapon (as most users are ). Most bolt-action firearms ...
. File:Bayonet-mount-01.svg, A rotating bolts locks in a way similar to a bayonet mount, such as shown here (but with much stronger lugs and locking grooves than shown) File:Rotating Bolt.png, Operation of a rotating bolt. File:ТОЗ-17 разобр.JPG, A
TOZ-17TOZ rifles are a family of .22 Long Rifle bolt-action cadet rifles manufactured by the Tula Arms Plant (Russian abbreviation TOZ stands for ''Tulsky Oruzheyny Zavod''). Most notably the TOZ-8, TOZ-17 and TOZ-78 which were used to train generations of ...
cadet rifle A cadet rifle is a rifle used by s and others for basic firearms and training. Generally .22 caliber and , they also come in versions. They are often miniature .22 caliber versions of standard issue s. Older 19th century cadet rifles w ...
chambered for
.22 long rifle The 22 Long Rifle or simply 22 LR (metric designation: 5.6×15mmR) is a long-established variety of 22 caliber22 caliber, or 5.6mm caliber, refers to a common firearms caliber, bore diameter of 0.22 inch (5.6 mm). Cartridge (firea ...
which has been disassembled. The bolt is locked by the bolt handle being dropped into a notch in the receiver. File:MauserSystem98Verschluss-03.jpg, A
Mauser 98 The Gewehr 98 (abbreviated G98, Gew 98, or M98) is a German bolt-action Bolt action is a type of manual firearm action of a typical double-barreled shotgun, with the action open and the extractor visible. The opening lever and the safety cat ...
bolt showing two locking lugs just behind the face of the
bolt Bolt or bolts may refer to: Implements and technology * Bolt (fastener) A bolt is a form of threaded fastener with an external male thread requiring a matching pre-formed female thread such as a nut. Bolts are very closely related to screw ...
. There is a third "emergency" lug in front of the bolt handle, in case the primary ones fail under pressure. In some designs the bolt handle itself may serve as the emergency "lug". File:Rugersrcarrier.jpg,
AR-15 An AR-15 style rifle is a lightweight semi-automatic rifle based on the ArmaLite AR-15 design, which is itself a scaled-down derivative of Eugene Stoner, Eugene Stoner's ArmaLite AR-10, AR-10 design. The then Fairchild (aircraft manufacturer), Fa ...

AR-15
bolt carriers showing multiple locking lugs on the bolts. File:AR-15 NIckel boron bolt.jpg, An AR-15 bolt stripped from the bolt carrier. File:SMLEAction.jpg, A Lee-Enfield Mk III rifle with the bolt pulled back. The bolt lugs lock into the receiver bridge and are rear-locking. File:Winchester1200Def-2.jpg, The
Winchester Model 1200 The Model 1200 and Model 1300 are two pump-action shotguns that were manufactured by the Winchester Repeating Arms Company, Winchester-Western Division of Olin Corporation. It was produced in 12-, 16- and 20-gauge (bore diameter), gauge. The mil ...
uses a rotating bolt. File:Browning BLR.jpg, The uses a rotating bolt
Rotating bolts can be adapted to automatic or semi-automatic designs and
lever A lever ( or ) is a simple machine A simple machine is a mechanical device that changes the direction or magnitude of a force In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge o ...
or pump actions. In these cases, the bolt is held by a bolt carrier. With the breech locked, an initial rearward movement of the bolt carrier causes the bolt to rotate and unlock. Similarly, when closing the breech, the final forward movement of the carrier causes the bolt to rotate and lock the breech. This action is commonly achieved by a slot cut in the carrier that engages a pin through the bolt perpendicular to the axis of the barrel. It is a type of linear cam. Straight-pull bolt-action firearms do not require the operator to rotate the cocking handle to cycle the action. Some straight-pull designs may use a rotating bolt but other breech-locking mechanisms can be employed.


Sliding block

The breechblock in a sliding block slides across the face of the breech to close it. The sliding action is perpendicular to the axis of the barrel. When the breechblock slides down to expose the breech, it is referred to as a falling block, as used in the Sharps rifle. A sliding block is common in artillery. A vertical sliding block rises and falls while an horizontal sliding block slides to one side. It is a strong design. The breechblock is well supported by the receiver within which it slides and the mechanisms for opening and closing the breech do not have to act to any extent against the forces generated on firing. Sliding-block-action.png , Operation of a sliding block. Sharps falling block action.jpg , Looking at the breech of a
Sharps rifle#REDIRECT Sharps rifle {{redirect category shell, {{R move{{R from other capitalisation{{R unprintworthy ...
Berdan Sharps rifle.jpg , Sharps rifle. Ruger no1 243 right open.jpg, Ruger No. 1 single-shot falling-block rifle in
.243 Winchester The .243 Winchester (6.2×52mm) is a popular sporting rifle A rifle is a long-barrelled firearm A firearm is any type of gun designed to be readily carried and used by an individual. The term is legally defined further in different count ...
with custom barrel with action open. 25 pounder breech CMHM Brantford.jpg , The open breech of an
Ordnance QF 25-pounder The Ordnance QF 25-pounder, or more simply 25-pounder or 25-pdr, was the major British field gun Field may refer to: Expanses of open ground * Field (agriculture) In agriculture, a field is an area of land, enclosed or otherwise, used for agricu ...
M101A1 Howitzer Breech and Carriage 20121013a.jpg , Breech of a M101A1 Howitzer.


Side-hinged breechblock

A side hinged breechblock is used in the Snider-Enfield and the Warner carbine. The breechblock is hinged parallel to the axis of the barrel and swings away to the side to expose the breech. Firing force is contained by the rear of the breechblock bearing on the receiver.


Trapdoor breechblock

Commonly associated with the
Springfield rifle The term Springfield rifle may refer to any one of several types of small arms produced by the Springfield Armory in Springfield, Massachusetts Springfield is a city in the state of Massachusetts, United States, and the seat of Hampden ...

Springfield rifle
, the breechblock is hinged above the breech face and lifts up like a trapdoor to expose the breech. The breech is locked by a catch operating at the end of the breechblock furthest from the hinge. It is similar in principle to a break-action.


Rolling block

A rolling block can be described as a quadrant which is hinged below the breech. The quadrant rotates through approximately 90° to provide access to the breech or close the breech. In the closed position, a number of different devices can be used to lock the quadrant and prevent it from opening. In the Remington Rolling Block rifle most closely associated with this type of breechblock, the hammer also has a quadrant which cams behind the breechblock and locks it. The
Spencer repeating rifle The Spencer repeating rifles and carbines were early American lever-action firearms invented by Christopher Miner Spencer, Christopher Spencer. The Spencer was the world's first military metallic-cartridge repeating rifle, and over 200,000 exampl ...
also uses a rolling block. Remington Rolling Block.jpg , The Remington rolling-block breech.


Peabody-Martini

Initially used in the Peabody rifle, it saw more widespread use in the
Martini–Henry The Martini–Henry is a breech-loading A breechloader is a firearm A firearm is any type of gun A gun is a ranged weapon designed to use a shooting tube ( gun barrel) to launch typically solid projectiles, but can also project ...
and the subsequent Martini–Enfield. It employs a breechblock with a rear hinged falling block design, in which the breech is opened by permitting the front of the breechblock to drop down while pivoting on its hinge. Firing force is transmitted through the knuckle of the hinge and does not act directly on the hinge pin. The breechblock design as has been called a falling or tilting block but in omitting the role of the hinge can lead to ambiguities. It is also used in the
Krag–Petersson The Krag–Petersson was the first repeating rifle adopted by the armed forces of Norway and was one of the first repeating rifles to be adopted as standard issue by a military force,
rifle. Martini henry lock section.png , Section of the
Martini–Henry The Martini–Henry is a breech-loading A breechloader is a firearm A firearm is any type of gun A gun is a ranged weapon designed to use a shooting tube ( gun barrel) to launch typically solid projectiles, but can also project ...
. Martini henry rifle 0213.png , The Martini-Henry, showing the breech open and closed. Martini Henry Mk I.jpg , The Martini-Henry Mk 1. Peabody rifle.jpg , The Peabody rifle, which has an external hammer.


Tilting block

As a tilting breechblock closes on the breech, it is tilted up at the rear but it drops into a recess at the end of its forward travel - thus locking the breech closed. Firing forces are transmitted to the locking shoulder at the rear of the recess. To unlock the breech, a slide or carrier moving rearward uses a wedge like arrangement acting on the sides of the breechblock to tilt it up at the rear and lift it clear of the locking shoulder. The breechblock is then pulled rearward by the slide or carrier to expose the breech. In the closed position. the slide or carrier can also help locate the breechblock in its locking recess. The carrier or slide can be operated by lever or pump actions or by gas, for automatic and semiautomatic fire.


In-line

The breech is opened by the breechblock moving in-line with the axis of the barrel and is locked in the closed position by an obstruction such as a cam, wedge, paw or over-centre levers. A roller lock is commonly associated with firearms produced by
Heckler & Koch Heckler & Koch GmbH (HK; ) is a German defence Defense or defence may refer to: Tactical, martial, and political acts or groups * Defense (military) A military, also known collectively as armed forces, is a heavily armed, highly organiz ...
. This type of breechblock can be adapted to cycle by lever, cocking handle or gas. The mechanism is usually designed so that a single action unlocks and then withdraws the breechblock using either a slide or levers. The M1895 Lee Navy is of this general type, even if the travel of the breechblock is not strictly in-line with the axis of the barrel. M1895 US Navy Straight Pull Rifle.jpg , The M1895 Lee Navy. Henry Rifle Receiver open.JPG , The
Henry rifle #REDIRECT Henry rifle #REDIRECT Henry rifle The Henry repeating rifle is a lever-action tubular magazine rifle famed both for its use at the Battle of the Little Bighorn and being the basis for the iconic Winchester rifle of the American American f ...

Henry rifle
uses a toggle to lock the breechblock in place.


Blowback

Blowback actions use an in-line breechblock in which the breech is never locked and is held closed by spring tension alone. They are used in semiautomatic and automatic firearms using low-powered cartridges. It is common in semiautomatic rifles and pistol chambered for .22 cal rimfire cartridges and many
submachine gun A submachine gun, abbreviated SMG, is a magazine A magazine is a periodical publication Periodical literature (also called a periodical publication or simply a periodical) is a category of serial publications that appear in a new edition ...
s. A variation is
blow forward 300px, The Mannlicher M1894 pistol, the first blow-forward firearm. Blow-forward is a firearm A firearm is any type of gun A gun is a ranged weapon designed to use a shooting tube ( gun barrel) to launch typically solid projectiles, ...
operation, in which the breechblock is fixed and the barrel moves.


Floating actions

In most longarms, the barrel is firmly attached to the receiver and does not move relative to the receiver during operations. Most semiautomatic pistols firing the higher powered pistol cartridges use a locked-breech design. The action is manually cycled by moving the slide rearward. The slide contains the breechblock and is initially locked to the barrel so that the combined assembly move together. A short movement trips the mechanism to unlock the barrel from the slide assembly, allowing the breech to open. When fired, recoil results in the same action. In many instances, the barrel and breechblock remain in-line. In the
Browning Hi-Power The Browning Hi-Power is a Trigger (firearms)#Single-action, single-action, semi-automatic firearm, semi-automatic handgun available in the 9mm and .40 S&W calibers. It was based on a design by American firearms inventor John Browning, and compl ...
and Colt's
M1911 pistol The M1911, also known as Colt 1911, or Colt Government, is a single-action A trigger is a mechanism Mechanism may refer to: *Mechanism (engineering) In engineering, a mechanism is a Machine, device that transforms input forces and movement ...

M1911 pistol
, the barrel is tilted slightly to release it from interlocking ribs, so in this respect, it may be likened to a tilting breechblock, even though it is the barrel and not the breechblock that tilts. This type of breechblock configuration and
recoil operation Recoil operation is an operating mechanism used to implement locked breech Locked breech is the design of a breech-reloading firearm's action (firearms), action. This is important in understanding how a self-reloading firearm works. In the simple ...
is not confined to pistols and may be found in machine guns and auto-firing cannons. 1911A1-JH02.jpg , A disassembled and showing the locking grooves on the barrel. Luger IMG 6761b.jpg, Swiss Parabellum Model 1900 Luger with breech opened, showing the jointed, toggle, locking arm in its most bent position. Locktab.jpg , Roller locks in the
CZ 52 The CZ 52 (also known by the Czechoslovak military designations vz. 52, for (vz. - ''vzor'' = model) "model of 1952", and CZ 482) is a semi-automatic pistol A pistol is a handgun, more specifically one with the chamber integral to its gun ...
pistol. When fired, slide and barrel move rearward but the locking piece in the slide is held by the tab indicated by the pointer.


Interrupted screw

Welin breechblock of a 16-inch Mk 6 gun on USS Alabama (BB-60), 1943. Note the four separate thread "steps" on the block which engage with matching steps in the breech when the block is swung up and inwards and then rotated slightly clockwise. The design allows thread to be machined on four-fifths of the circumference but requires only a one-fifth turn to disengage. A conventional interrupted thread would have thread on only half of its circumference and would need to be much longer to achieve the same strength. Perhaps a variation on the rotating bolt, an
interrupted screw Breech from Russian 122 mm M1910 howitzer, modified and combined with 105 mm H37 howitzer barrel An interrupted screw or interrupted thread is a mechanical device typically used in the breech of artillery Artillery is a class of h ...
provides greater strength than simple lugs while requiring only a partial rotation to release the breechblock. The Welin breech block, Welin breechblock is such a design and is used on weapons with caliber (artillery), calibres from about 4 inches up to 16 inches or more.


Falling screwed breechblock

The
Ferguson rifle The Ferguson rifle was one of the first breech-loading rifles to be put into service by the British military. It fired a standard British carbine ball of .615" calibre and was used by the British Army The British Army is the principal Army, ...

Ferguson rifle
used a tapered screw plug inserted perpendicular to the axis of the barrel. It was charged with ball and powder and required only one rotation to permit loading. While novel and effective, cost was a factor for its limited acceptance. Ferguson rifle.jpg, Ferguson Rifle.


Split breech

A less common type of breech is the split-breech design known as the "nutcracker". This type of breech consists of two counter-rotating
sprocket A sprocket, sprocket-wheel or chainwheel is a profiled wheel File:Roue primitive.png, An early wheel made of a solid piece of wood A wheel is a circular component that is intended to rotate on an axle An axle or axletree is a central ...

sprocket
s, with a temporary breech being formed where they touch. Relatively few guns have used this design. The prototype
Fokker-Leimberger The Fokker-Leimberger was an externally powered, 12-barrel rifle-caliber rotary gun developed in Germany during the First World War World War I or the First World War, often abbreviated as WWI or WW1, was a global war originating in Europ ...

Fokker-Leimberger
multiple-barreled machine gun used this design, but it had numerous problems with ruptured cases. Another "Fokker Split Breech Rotary Machine Gun, ca. 1930" was donated to Kentucky Military Treasures; according to the museum record it "proved unsuccessful because of its inability to seal breech cylinders". A couple of 1920s US patents by other inventors also proposed to use this principle. The British also experimented with the design in the 1950s for aircraft guns, without success. It has only been used successfully in low-pressure applications, such as the
Mk 18 Mod 0 grenade launcher image:Fast_Patrol_Craft_PCF-38_on_Cai_Ngay_canal_1970.jpg, A Mk 18 grenade launcher in use on a Patrol Craft Fast (on top of the dual .50 M2 Browning, M2 Browning machine guns) The Mk 18 Mod 0 was a 40x46mm grenade launcher used by the United Stat ...
.
/ref> In artillery the forces are much greater, but similar methods are used. The
Welin breech block The Welin breech block was a revolutionary stepped, interrupted thread design for locking artillery breeches, invented by Axel Welin in 1889 or 1890. Shortly after, Vickers acquired the British patents. Welin breech blocks provide obturation for a ...
uses an
interrupted screw Breech from Russian 122 mm M1910 howitzer, modified and combined with 105 mm H37 howitzer barrel An interrupted screw or interrupted thread is a mechanical device typically used in the breech of artillery Artillery is a class of h ...
and is used on weapons with caliber (artillery), calibres from about 4 inches up to 16 inches or more. Other systems use a , in which a solid block is slid across the open breech from the side or bottom to seal the opening.


See also

* :Firearm actions


References

{{Reflist


External links


Breech Mechanisms in artillery
Firearm components Firearm actions