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 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 pistols and shotguns. 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 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, 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 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
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 to set the correct headspace.Brownells - Fitted Barrel Instructions Correct mounting is important both for safety and accuracy.Custom Rifles | Warner Tool Company 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 and a vise. 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.“Blueprinting” (Truing) a Remington 700 Action – rifleshooter.com
Action threads
List of action threads M designates common V threads (like for instance metric threads) Sq designates square threads Tr designates trapezoidal threads 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".
Model Diameter (mm) Pitch (mm) Thread angle Shank length Comment Inch Smith & Wesson J Frame M12.70 0.706 mm 60° Also written as 0.500"-36 1/2"-36 Smith & Wesson K Frame M13.72 0.706 mm 60° Also written as 0.540"-36 69/128"-36 Smith & Wesson L Frame, Colt J, V, Colt AA Mark III / King Cobra, Colt Python (new), Colt Trooper (J, V, AA) M14.27 0.706 mm 60° Also written as 0.562"-36 9/16"-36 Colt Python (old), Colt E & I M14.31 0.794 mm 60° Also written as 0.5634"-32 9/16"-32 Destroyer 1921 carbine (Spanish) M15.88 0.977 mm 60° 15.88 mm 21.59 mm diameter at the shoulder 5/8"-26 Ruger GP-100 M15.88 1.058 mm 60° 5/8"-24 Remington Rolling Block No. 4 Rem. Action (solid frame model) M16.64 1.588 mm 90° 16.89 mm Also written as 0.655"-16. 21/32"-16 Mathieu Tr16.76 2.54 mm 29° 16.76 mm Trapezoidal threads. Also written as 0.660"-20 85/128"-20 Ruger Blackhawk M16.97 1.058 mm 60° Also written as 0.668"-24 43/64"-24 Smith & Wesson N Frame M17.02 0.706 mm 60° Also written as 0.670"-36 43/64"-36 Remington Rolling Block No. 4 Rem. Action (takedown model) ⌀17.15 (no threads) N/A 17.02 mm* Also written as 0.675". *Of which a length of 5.56 mm of the shank has its diameter reduced to 15.62 mm.27/40" Ruger Single Six series M17.26 1.058 mm 60° 87/128"-24 Colt Single Action Army Revolver (third gen)M17.35 1.058 mm 60° 17.75 mm Also written as 0.683"-24. Only 14.43 mm of the shank is threaded. 87/128"-24 Colt Single Action Army Revolver (first and second gen) M17.65 1.270 mm 60° 17.75 mm Also written as 0.695"-20. Only 14.73 mm of the shank is threaded. 89/128"-20 M1917 revolver M17.65 1.270 mm 60° Also written as 0.695"-20 89/128"-20 Ruger Redhawk M19.05 1.270 mm 60° 3/4"-20 Falling Block Works (FBW) Model K M19.05 1.588 mm 60° 25.15 mm 3/4"-16 Stiller SPF 2500X M19.05 1.588 mm 60° 3/4"-16 BSA Martini CadetBSA Martini Cadet 1 | Gunsmith Rod Henrickson M19.05 1.814 mm 55° 16.74 mm Maximum 25.40 mm shoulder 3/4"-14 Marlin 336, 1895 (.45-70) Sq19.69 2.117 mm 90° 21.59 mm Square threads 0.775"-12 Marlin 1895 (.450) M19.69 2.117 mm 60° 21.59 mm 0.775"-12 Ruger Mini-14 M20.64 1.270 mm 60° 13/16"-20 Colt AR-15 M20.64 1.588 mm 60° The barrel nut thread is M31.75 x 1.411 mm (1-1/4"-18) 13/16"-16 HK416, HK MR223, HK MR556 M21 1.5 mm 60° The barrel nut thread is M32 x 1.5 mm (1.26"-16.93) 0.827"-16.93 Remington Rolling Block No. 2 Rem. Action Sq21.59 2.117 mm 90° 30.48 mm* Square threads. Also written as 0.850"-12. *Of which a length of 10.16 mm of the shank has its diameter reduced to 20.45 mm17/20"-12 Remington Rolling Block No. 1-1/2 Rem., Sporting Action Sq21.59 2.117 mm 90° 36.65 mm* Square threads. Also written as 0.850"-12. *Of which a length of 12.70 mm of the shank has its diameter reduced to 20.32 mm 17/20"-12 Remington 1867 Navy pistol Sq21.59 2.117 mm 90° Square threads. Also written as 0.850"-12. 17/20"-12 Kimber M/84 M21.43 1.27 mm60° 27/32"-20 Sako L46/L-46 M21.72 1.588 mm 60° 21.46 mm Also written as 0.855"-16. 55/64"-16 Howa 1500 Mini Action M22 1.5 mm 60° Zastava M85 «Mini Mauser» M22 1.5 mm 60° 0.866"-16.93 Sako L461 M22 1.6 mm 60° 19.40 mm 0.864"-15.87 Mossberg MVP .223 M22.23 0.907 mm 60° Also written as 0.875"-28. 7/8"-28 Weatherby Mark V Varmint, Weatherby Mark V Varmintmaster M22.23 1.411 mm 60° 16.99 mm 7/8"-18 Cooper Model 22 M22.23 1.588 mm 60° 16.26 mm 7/8"-16 Savage Model 1920 Sq22.86 2.117 mm 90° Square threads. Also written as 0.900"-12. 29/32"-12 Browning BPCR, 1885Single Shot Rifles and Actions (1969), Frank de Haas M23.75 1.270 mm 60° 23.37 mm Also written as 0.935"-20. 15/16"-20 Winchester 1885 M23.75 1.588 mm 60° 23.37 mm 15/16"-16 Browning A-Bolt (early),Browning A Bolt | Gunsmith Rod Henrickson Browning BBR, Remington 7600 M23.81 1.270 mm 60° 15/16"-20 TAP-174, TAP-375 M24 1.0 mm 60° 19.75±0.05 mm 27.50 mm shoulder 0.945"-25.4 Sako AI/A1 (PPC, Vixen) M24 1.5 mm 60° 0.945"-16.93 Jalonen JJ-91 M24 1.5 mm 60° 0.945"-16.93 Keppeler M24 1.5 mm 60° 18 mm 0.945"-16.93 Loppo 1, Loppo 2 M24 1.5 mm 60° 20 mm 0.945"-16.93 Remington Rolling Block No. 1 Rem., Blackpowder Action Sq24.77 2.117 mm 90° 36.02 mm* Square threads. Also written as 0.975"-12. *Of which a length of 10.62 mm of the shank has its diameter reduced to 23.37 mm 39/40"-12 Mosin-Nagant M91/30 M24.64, M24.77 M24.89 1.588 mm, 1.588 mm, 1.814 mm 55/60° 23.88 mm 30.02 mm shoulder. Thread angle varies. 0.970"-16, 0.975"-16,0.980"-14 MAS M-1936 M24.89 1.588 mm 60° 21.46 mm Also written as 0.980"-16. 63/64"-16 Husqvarna 1640, M24.89 2.117 mm 55° 18.16 mm 27.94 mm shoulder. Also written as 0.979"-12. 63/64"-12 Mauser small ring: Mauser G33/40,Small Ring Mausers | Gunsmith Rod Henrickson Model 93, 94, 95 Swedish m/1896 and m/1938 M25 2.117 mm 55° 18.16 mm / 16.38 mm / 15.88 mm / 16.2+0.2 mm 24.89 mm major diameter. 27.94 mm shoulder 0.980"-12, 0.993"-12 Krag–Jørgensen, American model (US Krag-Jørgensen) Tr24.89 2.54 mm 29° 19.23 mm Also written as 0.979"-10. Trapezoidal threads, 24.89 mm shoulder 63/64"-10 CZ 527, BRNO FOX M25 1.25 mm 60° Also written as 0.984"-20.32. 1.024"-20.32 Krico 500, 700, M600, M700 M25 1.25 mm 60° 19.85-0.1 mm 28.00-0.05 mm shoulder 0.984"-20.32 Krico M-600, Tradewind 600 M25 1.270 mm 60° 20.32 mm 30.35 mm shoulder 0.985"-20 Lebel Berthier 8 mm M25 1.411 mm 55°/60° 25.53 mm 29.21 mm shoulder 0.985"-18 Varberger 717, 757, 777, Kongsberg Lakelander 389, Kongsberg 393 M25 1.5 mm 60° 19.75±0.05 mm 27.50 mm shoulder 0.984"-16.93 Heym SR 21, SR 30 M25 1.5 mm 60° 29.98 mm 29.25 mm shoulder, 5.90 mm loose recoil lug 0.984"-16.93 Nikko Model 7000, Golden Eagle Model 7000 M25 1.5 mm 60° 1"-16.03 FR F1 M25 1.5 mm 60° 22 mm Sako L57 / L-57 M25 1.5 mm, 1.588 mm 60° 21.46 mm 0.984"-16.93, 0.984"-16 Sako L-579, L579 Forester, L61 (early) M25 1.588 mm 60° 22.10 mm 1"-16 Mauser 8 mm (Siamese) M25 1.814 mm 55° 13.08 mm 27.94 mm shoulder 0.990"-14 Husqvarna 1600, 1900, 2000, 8000,Carl Gustaf 1900, Carl Gustaf 2000 M25 2.117 mm 55° 19.56 mm 27.94 mm shoulder 0.984"-12 Mauser 89 (Belgian) M25 2.117 mm 55° 19.3 mm 28.32 mm shoulder 0.985"-12 Mauser 88 (German) M25 2.117 mm 55° 18.29 mm 0.986"-12 Mauser Brevex Magnum M25 2.117 mm 55° 19.56 mm 0.988"-12 Mauser 91 (Argentine) M25 2.117 mm 55° 21.46 mm 33.66 mm shoulder 0.986"-12 Mauser 71/84"Bolt action rifles" (3rd edition 1995) by Frank de Haas, Part III: Reference - Barrel Shank Drawings, page 501-510 M25 2.117 mm 55° 21.59 mm 26.10 mm shoulder 0.987"-12 Farquharson rifle (Gibbs, Jeffery, and others) M25.07 1.814 mm 55°/60° 22.23 mm Also written as 0.987"-14. Thread angle varies with production year and manufacturer 1"-14 Husqvarna RB shotgun, RB M67 M25.10 2.117 mm 55°/60° 16 mm 0.988"-12 Kongsberg M60 jakt, M83, M83S, M83SK M25.23 2.117 mm 55° 16.2+0.2 mm Also written as 0.993"-12. Major diameter 25.23-0.2 mm. 1"-12 Krag–Jørgensen, Norwegian model Tr25.30 LH,Sq26.67 LH 2.117 mm 90°/29° 19.5+0.3 mm 29+0.1 mm shoulder. Left hand threads. *Trapezoidal threads on Steyr manufactured actions, also written as 0.996"-12 LH.Karl Egil (1998). Norske Militærgeværer etter 1867, side 191 *Square threads on Kongsberg manufactured actions, also written as 25.3-0.1 mm.Karl Egil (1998). Norske Militærgeværer etter 1867, side 132 1"-12 LH,1-1/16"-12 LH Browning A-Bolt (late) M25.40 0.794 mm 60° 1"-32 Mossberg MVP .308, Mossberg 100ATR, Mossberg ATR Night Train, Mossberg 4x4 M25.40 1.270 mm 60° 1"-20 Remington 788Remington 788 | Gunsmith Rod Henrickson M25.40 1.270 mm 60° 38.1 mm / 39.6 mm 1"-20 Ruger No. 1, M77, M77 MkIIRuger M77 Mark ll | Gunsmith Rod Henrickson M25.40 1.588 mm 60° 17.53 mm 35.56 mm shoulder 1"-16 Colt Light Rifle M25.40 1.588 mm 60° 1-16 FN FAL M25.40 1.588 mm 60° 1"-16 Ruger American M25.40 1.588 mm 60° 26.8 mm 1"-16 Ruger American Magnum M25.40 1.588 mm 60° 30.5 mm 1"-16 Ruger Precision Rifle (RPR) M25.40 1.588 mm 60° Timing via barrel nut M31.75x1.411 mm (1-1/4"-18 TPI). 1"-16 Winchester Model 70 (post 64)Winchester post 64 Model 70 | Gunsmith Rod Henrickson M25.40 1.588 mm 60° 17.78 mm 1"-16 Winchester 54/70 (pre 64) M25.40 1.588 mm 60° 18.8 mm 29.08 mm shoulder 1"-16 Winchester 54/70 (.22 Hornet) M25.40 1.588 mm 60° 21.21 mm 28.96 mm shoulder 1"-16 Tikka M55, M595, M695 M25.40 1.588 mm 60° 1"-16 Tikka T3,Tikka T3 | Gunsmith Rod Henrickson T3X M25.40 1.588 mm 60° 22.10 mm 1"-16 Sako L-61 (1. Mod.),