What is “lock time”?

by Tom Gaylord
Writing as B.B. Pelletier

This report covers:

How fast does black powder burn?
What is lock time?
Why does lock time matter?
Lock time for firearms
Rimfire cartridges were the problem
Summary

I’m writing this report because of a discussion we had on the blog a couple weeks back where readers were using the term lock time inappropriately. Don’t fret — most shooters do the same.

They were talking about the time a pellet stays inside the barrel of an airgun when it fires and calling it lock time. It isn’t. I promised then to address the subject and today is the day. Lock time relates only to a flintlock firearm.

How fast does black powder burn?

When it is unconfined, black powder that is used in black powder guns burns fast with a whoosh. It’s not as fast as photographic flash powder, but it is much faster than smokeless gunpowder. Here is a short video on photographic flash powder, to give you some idea of how fast that is.

Now black powder unconfined isn’t that fast, but it does burn quickly. When it is confined, such as when it’s packed inside a barrel, black powder detonates and burns at a rate of 11,000 f.p.s. That’s a little slower than half the speed of TNT, which burns at 22,700 f.p.s. when it detonates. TNT is called a high explosive and black powder is called a low explosive.

Now let’s look at the burning rate of unconfined black powder.

So, inside the firearm the speed of the black powder burning is near-instantaneous. It’s MUCH faster than smokeless powder that burns in a curve that changes as the internal pressure changes. But — and this is the whole point of today’s report — when not confined black powder burns much slower. It looks like a fast flash to us but it’s really much slower.

What is lock time?

Lock time is the term used to discuss how long a flintlock takes to ignite the main charge inside the barrel. It only refers to flintlocks — something I have to stress, because to use it any other way is to use it without meaning. Oh, two shooters can have a casual conversation and both understand what they are talking about when the term lock time is used, because they are both tacitly agreeing on what the term means. It would be like a shooter telling you his new .44 Magnum pistol had a lot of horsepower. You would know what he meant, even though a .44 Magnum pistol has very little real horsepower — maybe as little as 2. One horsepower is equal to 550 foot-pounds per second and a .44 Magnum bullet can develop 1,015 foot-pounds at the muzzle.

I used to own a .36-caliber flintlock rifle that had a very fast lock time. It was so fast that I could shoot that rifle accurately. I will explain why that was in a moment. However a few years ago I bought a flintlock fowler that has a much slower lock time. It is so slow that you can detect the difference between the flash in the pan and the ignition of the main charge. Let’s see that now.

I called it a rifle in the video but it is really a smoothbore fowler. That fact has no affect on lock time though.

Why does lock time matter?

You aim a rifle with the sights. Your sighting eye is wide open and focused on the front sight. It is also less than 12 inches from the flash in the pan that you saw in the earlier videos, where burning black powder throws burning embers all around. Your eyes are not safe when shooting a flintlock. Shooters who shoot flintlocks learn to close their eyes just before firing. If you expand the window to watch me fire the flintlock on full screen you will see that even though I’m wearing safety glasses I close my eyes just before the gun fires. If you watch the movie The Patriot, in the final battle between the continental army and the British redcoats you can see continental soldiers closing their eyes and even turning their heads to the side before firing their muskets. They were smoothbores anyway, so accuracy wasn’t as much of a big deal.

If the lock acts fast, the time between sighting for the final time and the gun firing will be short. If lock time is slow, like it is in the video above, that time will be longer and the shots will go wider.

If you have only fired a percussion muzzleloader, none of this will make any sense. As far as you are concerned, lock time is instantaneous. There is practically zero difference between a percussion gun and one that fires cartridges. But the first time you shoot a flintlock you’ll understand. Lock time matters!

The touch hole that connects the pan to the main charge in the barrel is the primary cause of slow lock times.  We are talking about times of 34-42 milliseconds for the gun to fire after the hammer starts to fall.

Flintlock shooters will drill out their touch holes and install liners that direct the fire from the pan to the main powder charge. There is even a custom gunsmithing service to speed up lock time! Flintlock shooters are as concerned about their touch holes as aigunners are about their air transfer ports.

Lock time for firearms

The lock time conversation spilled over into the rimfire target guns. Shooters wanted triggers that were lightning fast — as though the time the trigger took to act mattered. In 1930 Winchester changed the trigger on their Model 52 target rifle to a new “speed lock” design. Smallbore target shooters were convinced that faster ignition would lead to better scores. 

The Remington model 37 target rifle had the “miracle trigger.” The trigger blade did not move when squeezed, yet the rifle fired. They felt that this would eliminate rifle movement as the trigger was pulled.

Rimfire cartridges were the problem

The priming inside the rim of rimfire cartridges was to blame for their inaccuracy and still is today. Unless it is remarkably uniform, the cartridges don’t ignite in the same way every time and that is an offshoot of the lock time issue we have been discussing. It’s why air rifles have risen in some precision shooting sports (like BR-50 International).

Summary

Now you know what lock time is and why it matters. We need other terms for the time pellets remain in the barrels of our airguns after they fire.

42 thoughts on “What is “lock time”?


  1. I suppose in an air gun the “time” is really a “Discharge Delay.” That is, the time lag between the pull of the trigger releasing the sear that allows, at least on my many break barrels, the spring to force the piston to the end of its stroke and the consequent air pressure and velocity rise to move the pellet and then propel it out the muzzle. All of this is NOT, obviously, instantaneous and the interval allows the forces inherent in the weapon to move the muzzle off the POA. The shooter, during the Discharge Delay, must compensate for the movement and try and maintain the sight picture (in spite of what is going on) and thus the POA. The most effective compensation is the “Artillery Hold” advocated by our mentor, TG.

    I suspect that the same issues appertain to the PCP shooter. I have an multi-pump and single pump pneumatic and in each valves have to activate and compressed air move through them and channels to move the pellet and propel it out of the muzzle.

    Perhaps the difference in the “species” is found in a difference between the mechanical masses moving in a spring gun and the air mass moving in the PCP (and yes, there are mechanical movements in the PCP, but they allow the flow of air, they don’t cause it)?

    Incidentally, from time to time there are discussions of what constitutes an airgun vs. a fire arm. Maybe the simplest way to see it is that in the airgun, the weapon develops the power to move the projectile, whereas in the firearm, the ammunition itself develops the power?


    • LFranke,

      A most interesting dissertation, though I do think Yogi’s use of the term “Dwell Time” will be more suitable for us (well, at least me) as it uses one syllable words and it incorporates the word “time” which relates directly to our previously accepted term.

      The only “issue” I have is with your description of airarms and firearms arises when discussing PCPs and black powder muzzle loaders. Both require the addition of propellant. That may seem a bit “nit picky”, but some are.


      • RR,

        Even in a springer, when cocked,… you now have stored power,.. just the same as a PCP. Both have had an addition of deliberate action. Nothing happens with either until the trigger is pulled. They just deliver the push of air to the pellet in 2 different ways. “nit picky”,… yea I could see it getting a bit dicey. Best not go there. 😉

        Chris



  2. BB,

    Good article. That was my understanding. In my opinion, the link that Edw also applies (or some version thereof).

    It is like one word, spelled the same, that can have 2 different meanings. Same word, applied 2 different ways, to 2 different things.

    At the end, under Summary,.. you offer:

    “Now you know what lock time is and why it matters. We need other terms for the time pellets remain in the barrels of our airguns after they fire”.

    WELL? What would you offer? Dwell time, as Yogi suggest? If yes,.. do you then break up the dwell time into 2 parts,… like action and barrel?

    In Ed’s link, “lock time” is broken into 2 parts,.. 1) Action time and 2) Barrel time. “Action time” being highly variable because at one end we have springers with lots of metal driving forward and piston rebound,… and the other end, pneumatics, in which most cases is a small hammer being driven forwards, with a following air push.

    Chris


    • Chris,

      Since we can’t percieve miliseconds, I see no need for two terms. For us it’s the time betweeen the gun firing and the pellet leaving ths barrel.

      We also don’t perceive millions of neutrinos passing through our bodies every second. I am surprised someone hasn’t latched onto this fact as a sad back story to their lives yet!

      B.B.



      • You say we can’t perceive milliseconds.
        The human body and mind is actually very good at measuring/aligning things
        To a certain level.

        Your eye can perceive slight mis alignments, to an astonishing degree.
        Your sense of touch can tell a difference of mis alignment or difference in thicknesses within a few thousands of an inch.
        If you are extremely familiar with a song, you can tell when it’s a fraction of a second slower or faster than it’s supposed to be.
        Audiophiles can detect the minuscule wow and flutter in tapes or records.

        Even on your flint lock with the fast lock time, you could probably tell the difference in time when the pan charge had “wicked” into the flash hole, thereby slowing the ignition sequence every so slightly.

        Yes to people that haven’t shot flintlocks much, you put the pan charge in the pan, and when it ignites the flash will travel into the flash hole, and ignite the main charge.
        If the powder flows into the hole while carrying the rifle, it burns ever so much slower as the powder in the vent hole burns like a fuse instead of a flash..

        Yes we can not say “ it was 20 milliseconds slower”.
        But you do notice the ever so slight hangfire…


        • The brain can indeed perceive milliseconds. It is how we can tell the direction of sound.

          The time it takes sounds waves to travel from one side of your head to the other… is interpreted by the brain to indicate direction. You didn’\t consciously notice the delay. But your brain did. That’s how you know where the sound came from.

          Without that fractional perception of time, stereo or directional sounds would be useless.

          Kinda cool.

          StarboardRower


      • Ha ha, I for one lament the perpetual passage of subatomic particles through my body! With each passing moment, I am further stripped of my dignity. Woe is me!


  3. Well, don’t trust this, I’m going from memory. In the field of internal ballistics regarding firearms- lock time is the time from trigger release until primer ignition. There then is the ignition phase of powder generating expanding gases. Once the pressure builds to a level sufficient to overcome the projectile’s inertia and friction, you then have barrel dwell time until it leaves the muzzle. External ballistics now takes over. Modern pressure barrels used for testing firearms ammo can accurately map out these forces and actions.

    I wonder if any air gun or pellet manufacturer has ever invested in pressure barrel testing? I realize the ignition/combustion phase would not be present and thus the transducer would operate at a much lower pressure- 2000-4000 psi versus 40,000-60,000 psi perhaps. But factories turn out transducers everyday. Should be a plug and play operation.

    I think everyone has experienced what a damaged pellet skirt can do to your accuracy. Do we have a firm grip on the interplay of bore, leade, projectile shape and weight and the air required to get the pellet moving? How much pressure, when is it introduced, how quickly?, etc


  4. BB ,

    I like the term “Dwell Time ” good way to put it . I was taught there are 3 key things 1) Lock time , time for action to strike primer 2) Internal Ballistics , ignition until projectile leaves the barrel 3) External Ballistics , which is from muzzle to target . Dwell time is good because it is something that most people can relate to , maybe not the younger folks who never set points or tuned a lawnmower ! . I used to work with a guy who was an ex mechanic and he had never set points because when he started working on cars in 2000 everything was electronic controlled . Very interesting blog today , allot of food for thought .

    Gene Salvino


    • Gene,
      My dad was an auto mechanic and owned an auto repair shop from 1952 thru 1965. When I graduated high school he sold the business. I remember cleaning points with a points file, cleaning them with a post card, and setting with feeler gauges. Later we used a dwell meter, and I still have it in my tool box. I still have a timing light too. Last used it to set the timing on my old 1967 Cub Cadet tractor. I owned that old tractor for 40 years, finally trading it in for a new Cub in 2016. I never had to change the points in that old tractor. They were easy to work on because they were located under an external cover on the engine. I only cleaned and gapped them every few years. Yes, the maintenance was much more frequent on those old cars, but, they were also much easier to diagnose and work on. Today, you need a $5000 scanner to diagnose all the many computer modules on cars and trucks. Yup, those were the good old days. And, we didn’t even know that we were poor. 😉
      Geo (still safe in MI)


  5. BB ,

    Reminds me of the matchbook trick . Matchbooks are about 0.015″ thick . When I worked on small engines most guys just used a matchbook to gap the points since most were 0.016″ standard in small engines . I even remember filing points , cleaning with paper and would get them running . I still like modern engines with transistor ignitions , they are virtually maintenance free other than oil and air filters . A little nostalgia today .

    Gene Salvino


    • and did you also use cigarette paper between the points to verify when they would start to open, for timing? Ah, the good ole’ days. I love the new 100,000 mile spark plugs and electronic ignitions!

      Fred formerly of the DPRoNJ now happily in GA


  6. Interesting blog this morning BB!

    The first two videos reminded of when I did a thesis on rocket propellants. An open air burn test is actually quite informative but for more control I made a rocket motor test bed to collect the data. Had to smile at the steel wool flash powder igniter – been there, done that …developed my own coated wire igniter that worked well.

    Dwell time, like that term I always misused “lock time” myself but most people understand it. Whatever you call it, consistent accuracy requires a consistent delivery (hold) and a good follow thru is important. The shot “seems” to be instantaneous but it is not.

    Thanks for posting this – good to be reminded 🙂

    Hank


  7. Back in the 80’s I took a ballistics class.
    They covered internal, external, and Terminal ballistics. Or as our instructor put it “shooting, Kentucky windage, and wallop.”
    The “lock time” as we discuss here was covered in different class specific to each weapon. And was considered the time it took from the sear to release, until the ignition sequence started.

    Once I started tinkering on airguns, I have always considered the “dwell time” as the time the valve is open allowing the air or gas out of the valve into the barrel.

    As the pressure in the system changes, the amount of time the valve is open changes given the same force of the spring knocking the valve open.
    As the Pressure on the high side of the valve drops it will stay open longer.

    Once we start the projectile moving down the bore, we are into the same terms and math used in firearms

    Ian.


  8. Lock time is applied to other firing mechanisms besides flintlocks. It has to because firing a projectile is not instantaneous once the sear is tripped. Remington 700s have always been touted as great for target rifles because of the fast lock time.

    Brent



  9. Very interesting video on the flash photography.

    Photography has always been a big part of my life, but I had never thought much about the science of old flash photography.

    I have never researched the aspects of vintage flash photography, but I have used large format plate cameras with modern flash components.

    Did they actually mix the flash powder for each photo a kid then?
    I wonder if we as a modern perspective, we are overthinking how they did it back then.

    I had always thought they just put a charge of FFFF powder in the pan, adjusting more or less powder depending on the amount of illumination needed for a given Fstop, and lightning condition, and just set it off when they removed the lens cap.

    I also would have thought the ISO would have been much lower than 100.

    I have shot with ISO64 film, and the exposure time was much longer than say 100 or 200 given similar conditions.
    (For those not into photography, As your ISO number goes up, the film is more sensitive to light, but the image gets more grainy, but as the number goes down, the image is less grainy, but is more susceptible to motion blur, as your exposure time is longer.)

    But I am sure he is using commercially made modern plates.

    When we lived in Colorado, I became aquatinted with a photographer in Cripple Creek that did vintage photography, he would use modern commercial plates for photography that he would need a negative to make many photos from, and he would use a modern paper “plate” that was photo sensitive and would produce a positive image for 1 time photos of tourist family photos dressed up in western clothes.
    It was very enlightening..(pun intended.)


    • Bravo,
      I had forgotten all about the ISO films. Those were the day. Common choices here (in 35MM film) was 100, 200 & 400. There were more but these were the most likely you could find without going to a camera store. I liked 100 the best of those three just because I could take such clear pictures with it. Just had to be still and get the light right.

      Doc


      • In high school we shot night time football games on ISO400 Black and white 35mm. We also did our own film processing.

        We would “push process” the film.
        To be able to shoot at a faster shutter speed.

        We would set the ISO on the camera to 800, or occasionally 1600.
        And shoot the game, and in the development stage, we would use a formula to figure the longer time in the developer chemical to get a useable image.

        In the process you lost a lot of contrast, and it got very grainy.

        But hey, it was high school football.

        One photographer would shoot the action shots with the pushed process film, the other photographer would shoot the crowd and non action shots with flash and standard speed film.

        We shot basketball on medium format 2 1/4 x 2 1/4 twin lens reflex cameras.
        And large group photos with a 4×5 graflex.

        This thread brings back memories I had forgotten.

        Ian


        • I remember shooting Still Life and Portraits with Kodachrome ISO/ 6/9°, 25/15°, and 64/19° and the K14 Process. The 6 was a nightmare but the 25 gave results that made 64 seem like looking through a Vaseline smear! Never expected digital to ever get to the level it has! But it did. Of course i never dreamed to have 5 Terabyte of storage in my home Computer let alone in my Lap Top with computational speeds that stagger the mind! Back when my first personal computer was a Sinclair! And I used an IBM 360 at work.

          shootski


          • My first personal computer was a timex Sinclair, then a radio shack color computer. Then Commodore 64.

            Digital has still come a long way, but I think when you get to extreme low light, you still get some “noise” in the image.

            But I haven’t tried any of the really high end DSLR s in recent years.

            10 years ago I was working for a newspaper as their graphic artist, proof reader, prepress, and IT manager. (It was a small newspaper).
            I had to shoot a few games for the paper when things got busy, our sports reporter would shoot several hundred images per game.
            She used what I called the shotgun effect, shoot everything that moved, and then pick 3 images to publish.

            I grew up on film, I would shoot 30-60 shots per game. Composing the shots, figuring where the action was going to be, and shooting the action. I would end up with 20 or so good images to choose from,

            She would have 300 images to choose from, and only 6 or 8 would be good enough to publish…


            • I did a tour of duty at the Naval Photographic Center and got to play with a bunch of stuff in the ’70s. We also built the TARPS system after they killed a dedicated RF-14 photo bird. The resolution of the onboard systems was magical! The really high end DSLRs are amazing but the real magic is in the software used to manipulate the images. But i have a feeling that the Richness of film Photography will never be matched by digital sampling…just as it isn’t in the audio World; unless you have your own darkroom or know to play your LPs wet with a $1,000+ cartridge and record it to 2″ Ampex multichannel recorder at lots of IPS you should just download your tunes and pictures.

              I understand the method of holding the shoot button down letting that motor drive roll film and then hope you got a few Keepers. But then! I prefer to stalk closer and take my one shot too! Oh! that’s airgun hunting! But then i gather by your post you already knew that also!

              They won’t be listening to Music or looking at Photographs….but they can look at or listen to them without all the “work”. ;^)

              shootski


              • I wanted to say, that Sometimes, nothing beats film for certain practical effects.

                But didn’t want to be laughed off the blog.

                Digital effects are cheating in my opinion.

                But they are easier, and can do things we never could do with film

                You only have to be a photoshop wizard, not a photographer.

                What’s an advantage of film over digital photography?

                You ever see a digital camera run when the battery is dead?

                You can always guess the exposure with a mechanical camera.

                Ian.



  10. B.B.,
    I thoroughly enjoyed today’s report. I, too, have been misusing the term “lock time,” but I do like the new term “dwell time” that I see many prefer here. I really do hope you are planning a follow on to this report, as in, now that we have a new term (dwell time), perhaps you can educate us on the dwell time of various airgun platforms…yes, I’m really looking forward to something like that. =>
    Thanking you for all you do,
    dave



  11. B.B.,
    interesting about the lock time. When searching meaning of words/phrases and how we got them, makes me wonder if it’s even possible to “fire” an air gun since no “fire” is involved. “Firing” a gun looks like it came from China, involving “firing” of gun powder (to set fire) to propel the projectile. So really an air gun would be to shoot the gun. If we did that, some safety’s would have S and S instead of S and F (not good) lol.
    Also people get into the whole magazine vs clip thing. Funny Marlin used to sell 7 shot clips (said clip right on the package). But none of it bothers me.

    Thanks for another interesting topic

    Doc


  12. There are too many references to lock time being the interval from trigger release to primer ignition. Wikipedia is one of them and has a long list of firearms with fastest and slowest “lock times” coupled with a long list of references. I thought about posting it but not sure of the legality. You can easily look it up. The term lock time has been defined (incorrectly?) so often it has become standard sort of. We airgunners could agree that sear release to muzzle exit is the “dwell time” as suggested. There are lots of us!

    Deck


  13. B.B.,

    It is all Kleenex to me…the Dark Side has, however, used Dwell Time for the PCP valve open duration since the beginning!

    I offer: PRESS-TO-OUT shortened to:

    PRESTO

    from the Italiano! For FAST

    shootski


  14. B.B.,

    Really interesting read, thanks for sharing!

    I wonder to what degree “dwell time” influences the accuracy potential of various air rifles, especially big bores given their non-negligible recoil impulses. There must be some kind of relationship between lower dwell times and tighter group sizes up to a certain extent, all else held equal?

    WD


    • WD,

      In my experience shooting Big Bore, to include up to .58 caliber pistol and rifle, if the recoil is close to the same shot to shot, or at least predictable, then it really doesn’t matter. Consistency of internal ballistics if reasonable good always falls to the WIND! The movement of air during the external balistics phase (in my opinion and that of many other shooters) will always be the biggest factor in the accuracy equation for a shooter to overcome.

      Only one way i know to learn how; shoot in many different locations with wind from all corners of the Compass Rose! And always pay close attention and remember.

      shootski


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