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In firearms, barrel threads refer to the screw threads used to attach a
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, ...
. Action threads, also called receiver threads, are situated at the
chamber Chamber or the chamber may refer to: In government and organizations *Chamber of commerce, an organization of business owners to promote commercial interests *Legislative chamber, in politics *Debate chamber, the space or room that houses deliber ...
end of the barrel, and can be used for attaching the barrel to the receiver. The receiver normally has corresponding threads which are internal, with the matching action threads on the barrel usually being external threads. This design is most commonly used in rifles and revolvers, but also on some
pistol A pistol is a handgun, more specifically one with the chamber integral to its gun barrel, though in common usage the two terms are often used interchangeably. The English word was introduced in , when early handguns were produced in Europe, a ...
s and
shotgun A shotgun (also known as a scattergun, or historically as a fowling piece) is a long-barreled firearm designed to shoot a straight-walled cartridge known as a shotshell, which usually discharges numerous small pellet-like spherical sub- pr ...
s. This method of fixing a barrel to a receiver has been used extensively by firearms manufacturers since before the 20th century, and can be viewed as a traditional barrel mounting method. Action threads are not the only method of fixing a barrel to a receiver (see ''Alternative methods'' below). Furthermore,
recoil-operated 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 ...
firearm designs have moving barrels (e.g. most pistols or the Barrett M82 rifle). Muzzle threads are situated at the muzzle end of the barrel and can be used for mounting accessories such as a flash hider, suppressor or muzzle brake (compensator).


Designation

There are many systems for designating thread types ( metric, unified, Whitworth, etc.). Threading can be specified by diameter, pitch,
angle In Euclidean geometry, an angle is the figure formed by two rays, called the '' sides'' of the angle, sharing a common endpoint, called the ''vertex'' of the angle. Angles formed by two rays lie in the plane that contains the rays. Angles a ...
, length and fit tolerances. However, the use of action threads is not well standardized within the firearms industry, and threading can vary between manufacturers and models. For example, factory and aftermarket receivers using the
Remington 700 The Remington Model 700 is a series of bolt-action centerfire rifles manufactured by Remington Arms since 1962. It is a development of the Remington 721 and 722 series of rifles, which were introduced in 1948. The M24 and M40 military sniper ...
footprint are produced with various types of action threads, all with a diameter, but with a pitch of either a 1.588 mm (16 TPI, Remington standard), 1.411 mm (18 TPI) or 1.270 mm (20 TPI, Savage standard).Bolt Guns - a Survey of Rem 700 Custom Actions , RECOILWEB
/ref> Typically, many rifles use thread diameters in the range between . Many older rifles from the first half of the 20th century use a thread pitch around 2 mm (12.7 TPI), while many modern rifle use thread pitches around 1.5 mm (16.93 TPI). Fine threaded systems intended for hand tightening typically use thread pitches around 1 mm (25.4 TPI).


Mounting

Using action threads to mount a barrel to a receiver typically requires fitting by a competent gunsmith, and typically some machining has to be done. In this process it is important so set the correct headspace. Correct mounting is important both for safety and accuracy. If the barrel, receiver and bolt are not fitted properly, severe and potential fatal problems can arise due to faulty headspace, e.g. cartridge overpressure and case rupture. Threaded barrels are often mounted to the receiver with a lot of torque, and will therefore generally require tools for assembly and disassembly, such as a suitable action
wrench A wrench or spanner is a tool used to provide grip and mechanical advantage in applying torque to turn objects—usually rotary fasteners, such as nuts and bolts—or keep them from turning. In the UK, Ireland, Australia, and New Zeala ...
and a
vise A vise or vice (British English) is a mechanical apparatus used to secure an object to allow work to be performed on it. Vises have two parallel jaws, one fixed and the other movable, threaded in and out by a screw and lever. A vise grip is n ...
. Depending on the firearm, a recoil lug is sometimes fitted between the barrel and stock as part of the process, Cleaning up the receiver and barrel action threads is often done during "blueprinting" in order to increase accuracy.


Action threads


List of action threads

* M designates common V threads (like for instance
metric threads The ISO metric screw thread is the most commonly used type of general-purpose screw thread worldwide. They were one of the first international standards agreed when the International Organization for Standardization (ISO) was set up in 1947. Th ...
) * Sq designates
square thread The square thread form is a common screw thread profile, used in high load applications such as leadscrews and jackscrews. It gets its name from the square cross-section of the thread.Bhandari, p. 203. It is the lowest friction and most effici ...
s * Tr designates
trapezoidal thread Trapezoidal thread forms are screw thread profiles with trapezoidal outlines. They are the most common forms used for leadscrews (power screws). They offer high strength and ease of manufacture. They are typically found where large loads are re ...
s * The shank length is not always the same at the thread length, which is the case if the insert has a threadless portion (sub-shank) * Tenon designates the thread length * Shoulder designates the barrel diameter in front of the thread portion * Unless otherwise mentioned, right hand threads are assumed. Left hand threads are designated "LH".


Alternative methods

Several alternative mounting methods to using action threads exist. ;Barrel press fit: Pressing the barrel into the receiver to achieve a
press fit An interference fit, also known as a pressed fit or friction fit is a form of fastening between two ''tight'' fitting mating parts that produces a joint which is held together by friction after the parts are pushed together. Depending on the am ...
is an alternative to using action threads which has been used on firearms such as Anschütz Fortner, Anschütz Model 54,
AKM The AKM () is an assault rifle designed by Soviet small arms designer Mikhail Kalashnikov in 1959. It is the most ubiquitous rifle of the Kalashnikov rifles. It was developed as a replacement to the AK-47 introduced a decade prior. Introduced ...
and
Sauer 101 Sauer 101 is a bolt action rifle manufactured by Sauer & Sohn that was launched in 2013. The rifle is manufactured on the same factory and shares many parts with the Mauser M12. Technical The stock comes with a proprietary bedding system called ...
. ;Barrel nut: Attaching the barrel to the receiver using a barrel nut and a barrel with a shoulder is an alternative to action threads, which has been used in firearms such as the Sten gun and
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 ...
. ;Hand tools: Quick barrel change systems is an increasingly popular alternative, as seen in for example
SIG Sauer 200 STR The SIG Sauer 200 STR (Scandinavian Target Rifle), also known as the SIG Sauer 200 STR Match, is a bolt-action rifle mostly used as a target/competition rifle for national competitions by Norwegian, Swedish and Danish sport shooters. It is a var ...
, Roessler Titan or
Blaser R8 The Blaser R8 is a German straight-pull rifle known for its radially locking bolt system, modularity and its barrel mounted scope mount manufactured by Blaser. The rifle also features a manual cocking system and a direct trigger. In 2015 there ...
. These methods typically only require simple hand tools (like a hex key) or no tools at all. This can be an great advantage to competition shooters who regularly wear out barrels, or for hunters who want a modular rifle that can shoot several
caliber In guns, particularly firearms, caliber (or calibre; sometimes abbreviated as "cal") is the specified nominal internal diameter of the gun barrel bore – regardless of how or where the bore is measured and whether the finished bore match ...
s. In these designs, the bolt locks directly into the barrel, and the manufacturer often guarantees that the barrel is headspaced correctly from the factory. File:Charter Arms Explorer II takedown.jpg, A quick change barrel system using threads, intended to be assembled and disassembled without tools.


Muzzle threads

Muzzle threads is one method of fitting accessories such as flash hiders, suppressors or muzzle brakes (compensators). The applicable thread is limited to a certain degree by the bullet caliber and barrel diameter. Right-hand threads (RH) are most common, but left-hand threads (LH) are sometimes used instead. Unless otherwise stated, right-hand threads are usually assumed. In Europe it has become common to use 1 mm muzzle thread pitches. M14x1 is a common thread type on European hunting barrels, while M18x1 is common on competition bull barrels. A larger barrel thread diameter can improve the precision of the barrel. As of 2021, various Unified threads are still the de facto standard on most American firearms, such as 1/2"-28 (M12.7x0.907) on 5.6 mm (.223") caliber rifles and 5/8"-24 (M15.88x1.058) on 7.62 mm (.308") calibers. Some common barrel threads are listed below:Thread Pitch Guide - Thread-Pitch-Guide.pdf
/ref>


External threads on muzzle accessories

Some accessories, notably suppressors and concussion reduction devices (CRDs), attach via a muzzle device such as a flash hider, compensator, thread protector or sleeve.


See also

* Quick-change barrel system *
Press fit barrel In firearms, barrel threads refer to the screw threads used to attach a barrel. Action threads, also called receiver threads, are situated at the chamber end of the barrel, and can be used for attaching the barrel to the receiver. The receiver n ...


References


External links


Video of professional rifle barrel threading (YouTube)

Video of chasing out receiver threads on a Mauser 98 (YouTube)
{{Firearms Firearm terminology