Lock time

Lock time or action time refers to the time interval (often measured in milliseconds) from when the trigger of a firearm is activated until the firing pin strikes the primer, and depends on the design of the firing mechanism. A long lock time increases the probability of the shooter pulling the sights away from the target before the bullet has left the barrel, a common shooter error which can lead to poor hits or even misses. Shooters can therefore tend to experience better precision using firearms with a shorter lock time, and short lock times are especially sought after for shooting competitions which require high precision on small targets from unstable positions, such as the standing offhand position.

A firing pin and firing pin spring, whose design can greatly affect the lock time of a firearm.

Measuring lock time

The lock time can be measured electronically, but is often instead calculated mathematically by the manufacturer. Important mathematical design parameters taken into consideration is the spring constant (stiffness), firing pin weight as well as the weight of any other moving parts and length of movement.

The lock time of conventional bolt action rifles is usually around 2.6 to 9.0 milliseconds.[1] For example, the SIG Sauer 200 STR/SSG 3000 has a relatively short lock time of 2.4 ms.[2] Firearm mechanisms utilizing a hammer are known for having long lock times since the hammer becomes an extra moving part contributing to a longer lock time. For instance, the mil-spec AR-15 and HK416 triggers have a lock time around 10 ms.[3] Firearms with an electric primer can reach lock times close to zero milliseconds.

Lock time examples
Manufacturer and model Lock time
milliseconds
Rößler Titan 3, 6, 16 and Alpha[4] 1.6 ms
Savage 10 AccuTrigger[5] 1.6 ms
Anschütz 1827 Fortner[6] 1.7 ms
Sig Sauer 200 STR[2] 2.4 ms
Remington 700 (short action)[5] 2.6 ms
Winchester Model 70[6] 3 ms
Remington 700 (long action)[5][7] 3 to 3.2 ms
Ruger M77[6] 3.6 ms
M1917 Enfield[6] 4 to 5 ms
Mauser M98[6] 4 to 5 ms
M1903A Springfield[5][8] 5.7 to 6.5 ms
Lee–Enfield[9] 8 to 9 ms
AR-15/M4/HK416[3] approximately 10 ms

Improvement of lock time

Aftermarket part kits are available for several production rifles under names such as known as "speedlock". These kits reduce the lock time compared to the factory rifle by using a lighter firing pin and more powerful springs. While ordinary firing pins usually are made out of steel, speedlock firing pins are often either made of titanium or a mix of steel and aluminium, which in some cases can reduce the weight of the new firing pin to near half of the original. More powerful springs are used to further increase the firing pin velocity for further decreasing the lock time, as well as increase reliability since the new firing pin has less mass. On hammer fired firearms a more lightweight hammer and a more powerful hammer spring can also shorten the lock time, but a hammer fired firearm will still have a noticeable longer lock time than mechanisms without a hammer.[5]

Electronic trigger
Olympic champion Jin Jong-oh with his Steyr LP10E match air pistol featuring an electronic trigger system competing during the 2012 Olympics

To reduce lock time electronic trigger systems can sometimes be fitted instead of mechanical trigger systems. Electronic triggers systems are mostly found in high-end match arms and can reduce action time by about 90% or one order of magnitude.[10] At very low lock times the dwell time of the bullet or pellet becomes the most influential element. The lock time for an electronic firing circuit with electric ignition of a cartridge can be expected to be around 27 microseconds (0.027 milliseconds). Remington's Model 700 EtronX electronic firing circuit achieves a two orders of magnitude reduction compared to the standard Remington 700 rifle mechanical trigger mechanism.[11]

Not only the lock time determines how long time it takes from the trigger has been activated until the bullet has left the barrel. Both firearm and ammunition design impacts the time until ignition, time until maximum chamber pressure is reached, and the time the bullet spends travelling through the barrel. These can be summed up chronologically as follows:

  1. Lock time: The time from the trigger is activated until the firing pin hits the primer.
  2. Ignition time:[12] The time from the firing pin has hit the primer and until the powder has started to burn in such a way that pressure has formed inside the cartridge. (Reliable ignition and a consistent ignition time is sought after for both safety and precision.)
  3. Time until maximum pressure: The time from pressure has been created until maximum pressure is reached.
  4. Barrel time:[12] The total time the projectile spends travelling through the barrel. A "faster" cartridge in a short barrel can decrease the barrel travel time, thereby increasing precision.

Point 2, 3 and 4 describe the time from start of ignition until the bullet leaves the barrel, and can be summarized as the bullet dwell time.[13] In most modern fullbore centerfire rifle cartridges the total dwell time lies around 1.0 to 1.5 milliseconds, while the slower .22 Long Rifle round has a dwell time of around 2.3 milliseconds when fired from a smallbore biathlon rifle.[14]

See also

References
  1. Tubb Precision Speedlock Firing Pin - Rem 700 Short Action
  2. dfs.no - SigSauer - Produktbeskrivelse«Slagtid på tennstempel er 2,4 ms»
  3. "Geissele Hi-Speed National Match Trigger manual" (PDF). Archived from the original (PDF) on 2018-08-07. Retrieved 2018-12-08.
  4. titan6.com - Product Cataloge
  5. Locktime by Randy Wakeman
  6. Lock time by Bart Bobbitt
  7. Van Zwoll, Wayne (2012). Gun Digest Shooter's Guide to Rifles. Iola: Gun Digest Books. p. 58. ISBN 978-1440230721.
  8. Encyclopedia Of American Gun Design And Performance. Book I Rifles Section "Ignition", page 68
  9. Wadham, Rodger (2012). The 2012 Complete Book on Lee Enfield Accurizing B&W. lullu.com. p. 57. ISBN 978-1471603112.
  10. Lock Time – The Key to an Airgun’s Firing Cycle, http://daystate.com, August 3, 2018
  11. Remington's Model 700 EtronX Centerfire Target Rifle Redefines The Big Bang Theory, By Cliff Gromer, www.popularmechanics.com, Dec 7, 2004
  12. Encyclopedia Of American Gun Design And Performance. Book I Rifles Section "Ignition", page 170-171
  13. Petty, Charles E. (2000). "Adjustable Sights". American Handgunner. Archived from the original on 2004-11-21. Retrieved 2007-08-31.
  14. J.G. ANSCHÜTZ GmbH & Co. KG - Biathlon «With the extremely light firing pin with only 4 mm travel this rifle got an extremely short locktime of 4 ms, i. e. that the bullet left the barrel after 4 ms after the shot had been released by the trigger. It is of utmost importance for the shooter that the bullet leaves the barrel as fast as possible after shot release to reduce aiming mistakes.»
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