A breechblock (or breech block) is the part of the

firearm action In firearms terminology, an action is the functional mechanism of a breech-loading firearm that handles (loads, locks, fires, extracts and ejects) the ammunition cartridges, or the method by which that mechanism works. Actions are technically ...

that closes the breech of a

breech loading A breechloader is a firearm in which the user loads the ammunition ( cartridge or shell) via the rear (breech) end of its barrel, as opposed to a muzzleloader, which loads ammunition via the front ( muzzle). Modern firearms are generally breec ...

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). The first firearms originated in 10th-century China, when bamboo tubes ...

artillery Artillery is a class of heavy military ranged weapons that launch munitions far beyond the range and power of infantry firearms. Early artillery development focused on the ability to breach defensive walls and fortifications during sie ...

) before or at the moment of firing. It seals the breech and contains the pressure generated by the ignited

propellant A propellant (or propellent) is a mass that is expelled or expanded in such a way as to create a thrust or other motive force in accordance with Newton's third law of motion, and "propel" a vehicle, projectile, or fluid payload. In vehicles, the e ...

. Retracting the breechblock allows the chamber to be loaded with a cartridge. Breechblocks are categorised by the type or design of the mechanism by which it is locked or closed for firing. The firearm action more fully refers to the mechanism by which the operator actuates the opening and closing of the breech.

Variants

A way of closing the breech or chamber is an essential part of any

breech-loading weapon A breechloader is a firearm in which the user loads the ammunition ( cartridge or shell) via the rear (breech) end of its barrel, as opposed to a muzzleloader, which loads ammunition via the front ( muzzle). Modern firearms are generally bre ...

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 countries (see Legal definitions). The first firearms originated in 10th-century China, when bamboo tubes ...

. Perhaps the simplest way of achieving this is a

break-action Break action is a type of firearm action in which the barrel or barrels are hinged much like a door and rotate perpendicularly to the bore axis to expose the breech and allow loading and unloading of cartridges. A separate operation may be requir ...

, in which the

barrel A barrel or cask is a hollow cylindrical container with a bulging center, longer than it is wide. They are traditionally made of wooden staves and bound by wooden or metal hoops. The word vat is often used for large containers for liquids, u ...

forestock In firearms, the forearm (also known as the fore-end/forend, handguard or forestock) is a section of a gunstock between the receiver and the muzzle. It is used as a gripping surface to hold the gun steady, and is usually made out of heat-ins ...

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 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 rear of the breech for firing but be able to be retracted or otherwise moved for loading or unloading or to remove a spent cartridge. A breechblock is not a component of designs with multiple or moveable chambers such as

revolver A revolver (also called a wheel gun) is a repeating handgun that has at least one barrel and uses a revolving cylinder containing multiple chambers (each holding a single cartridge) for firing. Because most revolver models hold up to six r ...

s, harmonica guns, Kalthoff repeaters, Kammerlader rifles or, split breech designs. This article primarily addresses the matter of breechblock design, as opposed to the action, 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", in 1836. The Dreyse locked using the bolt handle ...

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 that is operated by ''directly'' manipulating the bolt via a bolt handle, which is most commonly placed on the right-hand side of the weapon (as most users are right-handed). Most bolt-actio ...

, in which the bolt is rotated and retracted by a handle attached to the bolt. In some designs, the handle (sometimes called a cocking handle) 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. 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 or Enfield is a bolt-action, magazine-fed repeating rifle that served as the main firearm of the military forces of the British Empire and Commonwealth during the first half of the 20th century, and was the British Army's sta ...

. 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-17 cadet rifle chambered for

.22 long rifle The .22 Long Rifle or simply .22 LR or 22 (metric designation: 5.6×15mmR) is a long-established variety of .22 caliber rimfire ammunition originating from the United States. It is used in a wide range of rifles, pistols, revolvers, smo ...

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 rifle made by Mauser, firing cartridges from a five-round internal clip-loaded magazine. It was the German service rifle from 1898 to 1935, when it was replaced by the Kar ...

bolt showing two locking lugs just behind the face of the bolt. 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 any lightweight semi-automatic rifle based on the Colt AR-15 design. The original ArmaLite AR-15 is a scaled-down derivative of Eugene Stoner's ArmaLite AR-10 design. The then Fairchild Engine and Airplane Corporatio ...

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 uses a rotating bolt. File:Browning BLR.jpg, The Browning BLR lever action uses a rotating bolt. File:Desert Eagle beside a box of Speer 325 Grain HP.jpg, The

Desert Eagle The Desert Eagle is a gas-operated, semi-automatic pistol known for chambering the .50 Action Express, the largest centerfire cartridge of any magazine-fed, self-loading pistol. Magnum Research Inc. (MRI) designed and developed the Desert Eagle ...

is a gas-operated, semi-automatic pistol using a rotating bolt. Rotating bolts can be adapted to automatic or semi-automatic designs and

lever A lever is a simple machine consisting of a beam or rigid rod pivoted at a fixed hinge, or '' fulcrum''. A lever is a rigid body capable of rotating on a point on itself. On the basis of the locations of fulcrum, load and effort, the lever is ...

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 a 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. File:Sliding-block-action.png, Operation of a sliding block File:Sharps falling block action.jpg, Looking at the breech of a Sharps rifle File:Ruger no1 243 right open.jpg, Ruger No. 1 single-shot falling-block rifle in .243 Winchester with custom barrel with action open File: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 and howitzer during the Second World War. Its calibre is 3.45-inch (87.6 mm). It was introduced into service just before the war started, combi ...

File:M101A1 Howitzer Breech and Carriage 20121013a.jpg, Breech of a M101A1 Howitzer File:Keilverschluss 1862.tif, upSection of the double wedge sliding breechblock of a C64 field gun, an early breech-loading field gun. The sliding breechblock consists of two opposed wedges. The screw mechanism moves the wedges relative to each other, to change the effective thickness of the breechblock. Expanding the block locks it in the closed position and seals the breech. File:Spencer rifle diagram.png, The

Spencer repeating rifle The Spencer repeating rifles and carbines were 19th-century American lever-action firearms invented by Christopher Spencer. The Spencer was the world's first military metallic-cartridge repeating rifle, and over 200,000 examples were manufacture ...

uses a falling breechblock (F) mounted in a carrier (E). Figure1, shows the breechblock raised. Firing forces are contained by the receiver at the rear of the breechblock. File:Spencer Carbine Mod 1865.JPG, The Spencer repeating rifle with the breech open. Before the breechblock carrier can "roll" downward, the breechblock must fall vertically to clear the receiver.

Side-hinged breechblock

A side hinged breechblock is used in the Snider-Enfield. Other firearms using this type of breechblock include the Warner carbine, the Joslyn rifle and the Tarpley 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. File:Snider breach open-extract.JPG, The opened breech on a Snider-Enfield showing operation of the ejector File:Joslyn rifle closeup.jpg, The side hinged breechblock of the Joslyn rifle

Rotating drum

A rotating drum breechblock or rotary breech consists of a cylinder which rotates on an axis offset from the barrel. It is also known as a cannon breech because of association with some cannon designs. A longitudinal cut-out section or eccentric hole provides access to the breech. Rotating the cylinder then closes the breech. The geometry is not unlike the cylinder of a

. In the M1867 Werndl–Holub, the cylindrical breechblock is retained at the rear by the receiver. Mating faces can be profiled (ie not faced perpendicular to the axis of rotation) so that the breech tends to seal or fit more closely as it is closed. the Nordenfelt eccentric screw breech is a variation of this design. Instead of holding the breechblock between the breech at one end and the receiver at the other, in this design the breechblock is threaded around its circumference and is screwed into the breech until it meets the rear of the chamber. The breech is opened by rotating it a fraction of a full turn, until a hole through the breechblock aligns with the bore. The Magnum Research Lone Eagle pistol is a single-shot pistol chambered for rifle cartridges that also uses a rotating drum breechblock. File:Colt Autentica.jpg, The geometry of a rotating drum breechblock is similar to the alignment of the cylinder and barrel of a revolver File:Wanzlbazaar.jpg, The rotating drum breechblock of the M1867 Werndl–Holub rifle Werndl rifle Bolt.gif, Animation of the Werndl rifle File:75mm1897BreechMechanismDiagram.jpg, Drawing showing the Nordenfelt eccentric screw breech mechanism of the 75 mm Field Gun Model 1897 M1 (US designation) File:Canon de 75 breech mechanism.jpg, Breech of the Model 1897 in the open position File:Schertz VFW 04.jpg, Breech of the Model 1897 in the closed position

Trapdoor breechblock

Commonly associated with the 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. File: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 single-shot rifle with a lever action that was used by the British Army. It first entered service in 1871, eventually replacing the Snider–Enfield, a muzzle-loader converted to the cartridge system. ...

and the subsequent

Martini–Enfield Martini–Enfield rifles were, by and large, conversions of the Zulu War era .577/450 Martini–Henry, rechambering the rifle for use with the newly introduced .303 British cartridge. Whilst most Martini–Enfields were converted rifles, a numbe ...

. 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 omitting the role of the hinge can lead to ambiguities. It is also used in the Krag–Petersson rifle. File:Martini henry lock section.png, Section of the

File:Martini henry rifle 0213.png, The Martini-Henry, showing the breech open and closed File:Martini Henry Mk I.jpg, The Martini-Henry Mk 1 File:Peabody rifle.jpg, The Peabody rifle, which has an external hammer File:Krag Petersson 1.jpg, The Krag–Petersson rifle uses a rear hinged falling block. The opening and closing of the breech is operated by the hammer. File:Krag Petersson 2.jpg, The Krag–Petersson rifle is fed from a tubular

magazine A magazine is a periodical publication, generally published on a regular schedule (often weekly or monthly), containing a variety of content. They are generally financed by advertising, purchase price, prepaid subscriptions, or by a combina ...

under the barrel. On cocking, a new round is presented to the open breech but must be manually inserted into the chamber.

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 or ramp-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. A tilting breechblock design is not confined to a tilt relative to the horizontal plane with the breechblock locking against the bottom part of the receiver (as described above). The FN Trombone uses a side locking design and the breechblock of the

Bren gun The Bren gun was a series of light machine guns (LMG) made by Britain in the 1930s and used in various roles until 1992. While best known for its role as the British and Commonwealth forces' primary infantry LMG in World War II, it was also used ...

locks against the top part of the receiver. The

M1895 Lee Navy The M1895 Lee Navy was a straight-pull, cam-action magazine rifle adopted in limited numbers by the U.S. Navy and Marine Corps in 1895 as a first-line infantry rifle.Walter, John, ''The Rifle Story: An Illustrated History from 1776 to the Present ...

is also of this type. The tilting action is achieved without a separate breechblock carrier but by the design of the cocking handle. When unlocking the breechblock, the cocking handle initially acts as a

crank Crank may refer to: Mechanisms * Crank (mechanism), in mechanical engineering, a bent portion of an axle or shaft, or an arm keyed at right angles to the end of a shaft, by which motion is imparted to or received from it * Crankset, the componen ...

with a

cam Calmodulin (CaM) (an abbreviation for calcium-modulated protein) is a multifunctional intermediate calcium-binding messenger protein expressed in all eukaryotic cells. It is an intracellular target of the secondary messenger Ca2+, and the bin ...

, which acts against the receiver to lift the rear of the bolt out of the locking recess. Further rearward pressure on the cocking handle then pulls the breechblock rearward. File:M1895 US Navy Straight Pull Rifle.jpg, The

File:FN Trombone.jpg, The FN Trombone is a pump-action rifle that uses a side-locking tilting block. File:FN Trombone breechblock (bottom view).jpg, The underside of an FN Trombone breechblock. As the action is closed, the rear of the breechblock is pushed sideways to lock in a recess in the side of the receiver. File:FN Trombone slide (top view).jpg, The slide of the FN Trombone (top view) is connected to the pump handle. The pin on the slide engages with the recess in the bottom of the breechblock to lock and unlock the breech. Cutaway_drawing_of_Bren_gun.png, A cutaway drawing of the Bren gun. It fires from an

open bolt A firearm is said to fire from an open bolt if, when ready to fire, the bolt and working parts are held to the rear of the receiver, with no round in the chamber. When the trigger is actuated, the bolt travels forward, feeds a cartridge from t ...

and is shown cocked, ready to fire. The Breechblock (24) is carried by the slide (18). The rear of the breechblock tilts up into a recess to lock it closed.

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, pawl or levers. A roller lock is commonly associated with firearms produced by

Heckler & Koch Heckler & Koch GmbH (HK; ) is a German defense manufacturing company that manufactures handguns, rifles, submachine guns, and grenade launchers. The company is located in Oberndorf am Neckar in the German state of Baden-Württemberg, and also ...

. This type of breechblock can be adapted to cycle by lever, cocking handle, gas or recoil. The mechanism is usually designed so that a single action unlocks and then withdraws the breechblock using either a slide or levers. The Henry rifle and subsequent

Winchester rifle Winchester rifle is a comprehensive term describing a series of lever action repeating rifles manufactured by the Winchester Repeating Arms Company. Developed from the 1860 Henry rifle, Winchester rifles were among the earliest repeaters. The M ...

s use an arrangement of levers referred to as a toggle, similar in operation to

locking pliers Locking pliers (also called Vise-Grips, a vice grip, Mole wrench or mole grips) are pliers that can be locked into position, using an "over-center" cam action. Locking pliers are available with many different jaw styles, such as needle-nose p ...

. The breechblock is held closed when the two levers forming the toggle are in-line. Flapper locking (as used in the

Degtyaryov machine gun The Degtyaryov machine gun (russian: Пулемёт Дегтярёвa Пехотный, Pulemyot Degtyaryova Pekhotny literally: "Degtyaryov's infantry machine gun") or DP-27/DP-28 is a light machine gun firing the 7.62×54mmR cartridge that was ...

) uses metal plates on either side of the breechblock that "flap out" like barbs on an arrow and lock into recesses in the receiver. The flaps can be retracted parallel to the block for unlocking. The straight-pull Heym SR 30 uses ball bearings for locking, similar to an air fitting connector. The Blaser R93, another straight-pull action, is similar. It has a locking collet that consists claw-like segments instead of ball bearings. The multiple claws provide a large contact area to distribute load. These are arranged radially around the axis of the bolt. They extend to lock the bolt by engaging with an annular groove in the barrel behind the chamber and are retracted to unlock the bolt. File:Locking pliers.jpg, The toggle lock of many lever-action rifles is similar to the mechanism of locking pliers. The pliers lock when the toggle mechanism is pushed over-centre. File:Henry Rifle Receiver open.JPG, The Henry rifle uses a toggle to lock the breechblock in place. EB1911 - Machine Gun - Fig. 9.—Maxim Gun Mechanism.jpg, The

Maxim gun The Maxim gun is a recoil-operated machine gun invented in 1884 by Hiram Stevens Maxim. It was the first fully automatic machine gun in the world. The Maxim gun has been called "the weapon most associated with imperial conquest" by historian ...

employs a toggle-lock mechanism.. File:Mannlicher Gewehr.jpg, Drawing of Mannlicher M1886 rifle is a straight-pull action. The bolt is locked in place by a wedge (D). It is retracted up by the bolt carrier as the cocking handle (part of the bolt carrier) is initially pulled rearward.Bolt Disassembly Austrian Mannlicher 1886/1888/09
accessed 9 July 2021. 1943 Mauser P.38 Locking Block.jpg,

Walther P38 The Walther P38 (originally written Walther P.38) is a 9 mm semi-automatic pistol that was developed by Carl Walther GmbH as the service pistol of the Wehrmacht at the beginning of World War II. It was intended to replace the costly Luger P08, ...

employs a wedge-shaped hinged locking piece underneath the breech. File:Air fitting locking mechanism.jpg, An air fitting locking mechanism. Roller or ball locking mechanisms are similar in operation to this air fitting. In this case, the locking piece is a sleeve (i.e. outside) but the design can be transposed so that the locking piece acts from the inside position. File:Heym SR 30 Straight Pull Bolt Action.jpg, Disassembled bolt of the Heym SR 30

Blowback

Blowback actions use an in-line breechblock in which the breech is never locked and is held closed by spring tension alone. The force of the discharge is contained by a combination of spring force and the mass of the breechblock. 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 (SMG) is a magazine-fed, automatic carbine designed to fire handgun cartridges. The term "submachine gun" was coined by John T. Thompson, the inventor of the Thompson submachine gun, to describe its design concept as an automa ...

s. A variation is

blow forward Blow-forward is a firearm action where the propellant gas pressure and the friction of the bullet traveling down the bore drag the whole gun barrel forward to facilitate the opening of the breech. This forward barrel motion provides most of t ...

operation, in which the breechblock is fixed and the barrel moves.

Delayed blowback Blowback is a system of operation for self-loading firearms that obtains energy from the motion of the cartridge case as it is pushed to the rear by expanding gas created by the ignition of the propellant charge. Several blowback systems exist ...

uses additional mechanical devices that retard or delay the rearward movement of the breechblock; however, the breechblock is not locked in place by such devices. It allows a lighter mechanism compared with simple blowback.

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 single-action, semi-automatic pistol available in the 9×19mm Parabellum and .40 S&W calibers. It was based on a design by American firearms inventor John Browning, and completed by Dieudonné Saive at FN Herstal ...

and Colt's

M1911 pistol The M1911 (Colt 1911 or Colt Government) is a single-action, recoil-operated, semi-automatic pistol chambered for the .45 ACP cartridge. The pistol's formal U.S. military designation as of 1940 was ''Automatic Pistol, Caliber .45, M1911'' for ...

, 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 floating configuration and

recoil operation 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 ...

is not confined to pistols and may be found in machine guns and auto-firing cannons. 1911A1-JH02.jpg, A M1911A1 pistol 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 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

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 guns. It is believed to have b ...

provides greater strength than simple lugs while requiring only a partial rotation to release the breechblock. The Welin breechblock is such a design and is used on weapons with calibres from about 4 inches up to 16 inches or more. The Ross rifle Mk III is a straight-pull design that has multi-thread locking lugs. File:Sailor looking into the breech of 16 inch gun aboard USS Alabama (BB-60).jpg, 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. File:Ross Mk II - Mk IIISB2007.jpg, Mechanism comparison between Ross Mk III (1910) with multi-thread locking lugs and Mk II** (1907) with two solid lugs, similar to a

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 in the American Revolutionary War at the Battle ...

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. File:Ferguson rifle.jpg, Ferguson Rifle

Notes

References

External links

Breech Mechanisms in artillery
{{Firearms Firearm components Firearm actions