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.

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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.