Lock Time?

[Tom68]

Here is a topic of which I have only passing knowledge. My understanding is that it is the time from which the sear is released until the firing pin completes its forward travel, and it is measured in microseconds. If this definition is incorrect, please let me know.

More importantly, what is the effect of lock time on ability to hit a target? I would reason that a more precise firing mechanism with a shorter lock time COULD reduce movement of the firearm prior to the bullet exiting the bore, but I can see where that may not always be the case.

As an example, I just purchased a Spanish M1916 carbine (I have not yet fired it, but I'm not expecting great accuracy here...). The cocking indicator at the rear of the bolt travels about 2 inches (okay, so that's an exaggeration, but it is an unusually long distance compared to other bolt actions that I own). I can bet there is a lot of slop within that movement that would at least have SOME effect on the stability of the firearm during the firing sequence. I could conceive some sort of relationship between lock time and the amount of movement during the sequence. If so, is this "slop" measurable? If so, how? And for that matter, what device is employed to measure lock time?

I know this is a question for the 100 lb. brains on the forum and will get lots more views than replies... but I will bet that there are a lot of us who do not understand this very well.

[kraigwy]

Concentrate on follow through and don't worry about lock time.

Worrying about it will cost you more points then lock time itself.

[Tom68]

Honestly Kraig, lock time is the last thing on my mind when shooting

I was just hoping somebody'd have a technical explanation that would satisfy my morbid curiosity. When I read in an advertisement or a review extolling the virtues of some rifle's outstandingly fast lock time, I'm just wondering exactly what the writer intends to convey as the benefits of said characteristic.

I always enjoy reading your posts, by the way.

[B.L.E.]

The shorter the lock time, the less time there is for the gun to move off aim during the firing process.
Also, if you have a heavy and slow hammer, the reaction to the hammer fall can cause considerable movement during the hammer fall along with the sudden release of pressure on the trigger finger. This can result in a significant change of point of impact depending on whether the gun is lightly or loosely gripped by the shooter.
You can see this if carefully dry fire a single action revolver that has a scope on it. When that hammer drops, you will see the image jump, even on sandbags.

I found this out when I was shooting a flintlock pistol at a target. Even though I wasn't jerking the trigger or flinching, a lot of my shots went low, way low, nearly missing the paper. What was happening was the sudden release of the trigger pressure was allowing the barrel to drop during the ignition time. I firmed up the grip of my middle, ring and little fingers so that my index finger's only job was to move the trigger and that problem went away.
On a modern target pistol with a fast lock time and almost no trigger backlash, I probably would never have discovered how the grip was affecting accuracy and point of aim.

[wpsdlrg]

Lock time is measured in MILLIseconds (thousandths of a second)....NOT MICROseconds (millionths of a second). Even the slowest actions of all, such as old milsurps like Mausers, Mosin Nagants, etc. still have lock times of less than a 1/100 of a second.

Nevertheless, as kraigwy said, you should concentrate on shooting fundamentals.....and forget about lock time. For anything other than open class, long range target shooting, it doesn't really matter.

[4EVERM-14]

Lock time will be of concern to the high level competitive shooter particularly in the standing position. Being the least stable platform the shooters movements show up on the target more then other positions. Since no one can stand perfectly still releasing the trigger when the sight picture is failing is not desirable but still occurs. A fast lock time can sometimes save a poor shot from being a really bad shot. Someone who shoots competitively at incredibly small targets six days a week will notice how lock time effects their game. But for us mortals, like kraigwy and BLE posted, worrying about lock time is a moot point.

[MrBorland]

Originally Posted by B.L.E.

Also, if you have a heavy and slow hammer, the reaction to the hammer fall can cause considerable movement during the hammer fall along with the sudden release of pressure on the trigger finger. This can result in a significant change of point of impact depending on whether the gun is lightly or loosely gripped by the shooter.
You can see this if carefully dry fire a single action revolver that has a scope on it. When that hammer drops, you will see the image jump, even on sandbags.

Here's a vid that demos this effect. Well, it actually demonstrates the opposite - that a light & fast hammer helps prevent muzzle jar upon hammer strike.

http://www.youtube.com/watch?v=lmy5mkjpUNI

Originally Posted by 4EVERM-14

But for us mortals, like kraigwy and BLE posted, worrying about lock time is a moot point.

As I understand it, the AR15's got a relatively long lock time - wouldn't a high speed trigger (e.g. Geissele) offer a real benefit when target-grade accuracy matters? Is it standard equipment in highpower competition, for instance? Just curious.

[B.L.E.]

I was trying to shoot small groups with a Ruger #1 single shot rifle from the bench and as I squeezed the trigger and the sear released, the hammer fell but the round did not go off.
The image in the scope jumped a couple of inches from the vibration caused by the hammer fall. I dry fired it on purpose again just to see that again. That kind of explains why that gun can shoot small groups but it's very sensitive to what point you rest the gun on and how firmly the stock is held.
Suddenly, a lightened hammer makes sense, and there is an aftermarket lightened hammer available for these rifles.

An extreme example of a gun that jumps due to "hammer fall" is a spring air rifle. Virtually all of these gun's recoil is due to the motion of the piston that compresses the air as the gun fires. In order to get consistant point of impacts out of these, the shooter has to learn to hold it in a consistant manner and just allow the gun to move unhindered during its firing cycle.

[Bart B.]

There's two "times" critical to accuracy. Both are typically measured in thousandths of a second. This thread's about the most common one, how long it takes from when the sear releases the firing pin (or hammer) and when the firing pin strikes the primer.

The other one's "barrel time." How long it takes from the firing pin impacting the primer to when the bullet exits the barrel. For a given centerfire cartridge and load, the longer the barrel the longer the barrel time. It's typically between 2 and 3 milliseconds. .22 rimfire ammo's longer; they shoot slower.

An interesting thing was done some years ago for high end match rifles made in Germany. Anschutz (well known in international rimfire competition) had developed the fastest trigger-firing pin system on earth; a bit over 1 millisecond lock time. But their 26 inch barrels had a long barrel time. It was hard for the kids on Olympic teams to shoot goood scores from standing. They had to hold still seemingly forever after the sear released. So Anschutz shortened the barrels to about 19 inches which greatly reduced barrel time. A tube was added to extend the front sight back to the original sight radius.

Now the Anschutz barrels are back to 26 inches. I've no idea why. Maybe it's an accuracy issue.

[MrBorland]

Originally Posted by Bart B.

Now the Anschutz barrels are back to 26 inches. I've no idea why. Maybe it's an accuracy issue.

My WAG: .22LR SV is fastest when it only has 16-18" of barrel to traverse. If standard velocity ammo begins flirting with supersonic velocities from 19" barrels, then, the buffering effect of a 26" barrel may lead to more consistency.

[Tom68]

Now we're getting somewhere... a discussion about a topic I simply wanted to learn more about that I hadn't seen written elsewhere. I really had no intentions of "doing anything with" this knowledge... but to be candid I was getting a little discouraged with the replies of "don't worry about it"

Keep 'em coming, folks, I'm always interested in learning something new. Barrel time, for example, is a notion that I do understand, having been educated on that before on this here board... but a corollary to my original question, by what method or equipment is lock time and barrel time measured?

Once again, just my morbid curiosity at work.

[NoSecondBest]

I don't think there's anything that demonstrates more the insignificance of lock time than watching some very highly skilled shooters shooting their 1874 Sharps rifles at six hundred yards. These guns are side hammers and have very slow lock times and the bullets are really SLOW. Some of these guys are shooting MOA at six hundred yards in competition. With black powder and iron sights! Don't get too hung up on lock time, there's a lot more important things to concentrate on.

[MrBorland]

Originally Posted by NoSecondBest

I don't think there's anything that demonstrates more the insignificance of lock time than watching some very highly skilled shooters shooting their 1874 Sharps rifles at six hundred yards.

"Insignificance" or "significance"? If lock time were insignificant, why does it take "highly skilled" shooters to shoot a Sharps at 600? Isn't it likely these shooters would tell us that it is these conditions (slow bullet & lock time) that provide a particularly tough added challenge.

Originally Posted by Tom68

I really had no intentions of "doing anything with" this knowledge... but to be candid I was getting a little discouraged with the replies of "don't worry about it"

I'm all for curiosity. Some might presume it means the asker is merely looking for a short cut around good technique. There is no short cut, of course, but knowledge strengthens one's foundation, IMO.

[4EVERM-14]

As I understand it, the AR15's got a relatively long lock time - wouldn't a high speed trigger (e.g. Geissele) offer a real benefit when target-grade accuracy matters? Is it standard equipment in highpower competition, for instance? Just curious.

The stock AR trigger does needs work to break clean. Which I think takes precedence over lock time. Once done the rifle can still be equal to faster systems. That said, I have experienced shots I gave up on because of poor technique that were saved by Geissele's faster lock time.
But great scores have been fired with slow systems which is why I say fundamentals and technique are more important. In the end it is the 'nut behind the trigger' that's responsible.
As to faster lock times the hammer or striker is usually a lighter weight material. As such they need stronger springs to drive positively into the primer. Many ,like the Geissele, have completely different throws and sear geometry from the stock assemblies. They can be more fragile in that more attention may be needed to keep them operating properly. Falling out of adjustment is an occasional malady.

[MrBorland]

Originally Posted by 4EVERM-14

As to faster lock times the hammer or striker is usually a lighter weight material. As such they need stronger springs to drive positively into the primer.

I often hear this about revolver hammers. The problem is (at least in the case of revolvers) it ain't so: Lighter hammers don't need stronger springs to maintain reliability. I'm trying to understand why an AR hammer would be different.

The popular assumption is that a revolver's hammer's momentum or energy sets off primers. But it's neither momentum nor energy that sets primers off. It's the hammer's power. A lighter hammer gains speed (and therefore power) if the spring remains unchanged. IOW, it's better at igniting primers. Matter of fact, you can lighten a revolver's mainspring without affecting reliability if you bob the hammer. And with less hammer jar to boot. Check out my vid above. That revolver has a competition-grade DA trigger pull, but it's lit off everything I've fed it. And it's a tack driver to boot.

[B.L.E.]

I figured it's the amount of energy needed to cock the spring that determines how much energy the hammer has. A lighter hammer will simply be accelerated to a higher velocity resulting in nearly the same energy.

I see a lot of Ruger Old Army cap and ball revolvers sporting lightened hammers in black powder target competition. Usually drilled full of holes like swiss cheese. I think bobbing the spur would be more effective since the mass of the spur is so far away from the pivot point, but then you'd have no good way to cock it.

[MrBorland]

Originally Posted by B.L.E.

I figured it's the amount of energy needed to cock the spring that determines how much energy the hammer has.

Yes - the spring, not hammer mass, determines the energy of the hammer strike. But energy only has the potential to do work, so how it's applied to the primer is critical. To dent the primer, all that energy needs to be applied fast. That's power. Pushed by the same spring, a lighter, faster hammer delivers more power (with less momentum) to the primer (shorter lock time, too). Imagine a hand-held hammer meeting your car's bumper - the lighter, faster one is more likely to leave a more defined dent.

Originally Posted by B.L.E.

I think bobbing the spur would be more effective since the mass of the spur is so far away from the pivot point, but then you'd have no good way to cock it.

Yes - not all hammer mass is the same. Mass that's farthest from the pivot will have the greatest effect on hammer speed & lock time when it's removed. One of the advantages of going DAO on a DA/SA revolver.

[Bart B.]

For what it's worth, folks thinking that a short lock time's not important for best accuracy, maybe they should figure out how much an arm's aiming poiint moves around from less stable positions. Standing, without any support or steadying device whatsoever.

Then, just maybe, they'll understand why scores shot in competition from prone are higher, much higher than in standing; and sitting and kneeling are in the middle range.

[NoSecondBest]

Insignificance" or "significance"? If lock time were insignificant, why does it take "highly skilled" shooters to shoot a Sharps at 600? Isn't it likely these shooters would tell us that it is these conditions (slow bullet & lock time) that provide a particularly tough added challenge.

Your ignorance is showing here. These shooters are shooting bullets weighing in at over 500 grains with multiple feet of drop and open sights. Your simply challenging anyone's opinion that doesn't support yours.

[MrBorland]

Originally Posted by NoSecondBest

Your ignorance is showing here. These shooters are shooting bullets weighing in at over 500 grains with multiple feet of drop and open sights. Your simply challenging anyone's opinion that doesn't support yours.

Sorry - I'm not challenging your opinion - just trying to learn.

Your first post seemed ambiguous, so I was asking for clarification: On one hand, it argues for the insignificance of lock time because platforms with long lock times can be shot accurately. OK, I get it. But it also seems to argue that "very highly skilled shooters" are so good, they can make the shot despite the long lock time. IOW, lock time does matter, and it takes a highly skilled shooter to deal with it.

[tobnpr]

Lock time is an important consideration, as with any aspect of trigger control as it relates to accuracy- it becomes more evident as range increases.

When you consider how difficult it is to achieve the "perfect" trigger press- respiratory pause, between heartbeats if you're good enough...the shorter the time you need to maintain that with no movement, the better...

[Scorch]

Now the Anschutz barrels are back to 26 inches. I've no idea why. Maybe it's an accuracy issue.

With match rifles that use iron sights, it is a sight radius issue, the longer sight radius gives better accuracy. In a match, that is important.

the spring, not hammer mass, determines the energy of the hammer strike

Kinetic energy= 1/2 mass X velocity squared
Momentum = mass X velocity

You may notice in both equations, mass figures prominently. The mass of the hammer is the primary cause of induced vibration. In older cartridge rifles, the mass of the hammer is a carryover from percussion rifles, heavy leaf springs, and thick primer cups. John Browning demonstrated that the heavier hammers were not necessary, his 1878 design that became the Winchester 1885 High Wall had a much lighter hammer, and dominated target shooting in the last decade of the 1800s, beating out the Sharps, Remingtons, Ballards, Wessons, and Marlin rifles.

I was trying to shoot small groups with a Ruger #1 single shot rifle from the bench and as I squeezed the trigger and the sear released, the hammer fell but the round did not go off.
The image in the scope jumped a couple of inches from the vibration caused by the hammer fall. I dry fired it on purpose again just to see that again.

Yes, Ruger #1s have a large, heavy hammer. Consequently they have a lot of vibration caused by the hammer fall.

The shorter the lock time, the less time there is for the gun to move off aim during the firing process.
Also, if you have a heavy and slow hammer, the reaction to the hammer fall can cause considerable movement during the hammer fall along with the sudden release of pressure on the trigger finger.

Do not confuse cause and effect. Slow lock times with heavy strikers causes large amounts of vibration, which translates into POI movement because they casue the barrel to move. You will have little time to move your muscles very far during hammer fall, but the movement casued by the movement of the heavy hammer is immediate and noticeable.

There's two "times" critical to accuracy.

Correct, Bart. I usually hear them referred to as lock time and dwell time, but terminology is irrelevant. Lock time affects accuracy by reducing the movement possible during striker fall, dwell time affects movement during bullet travel in the bore. You want both to be short and vibration-free. This is one of the reasons benchrest shooters want fast locktimes, light weight strikers, and fast cartridges.

[MrBorland]

Originally Posted by Scorch

Kinetic energy= 1/2 mass X velocity squared
Momentum = mass X velocity

You may notice in both equations, mass figures prominently. The mass of the hammer is the primary cause of induced vibration. In older cartridge rifles, the mass of the hammer is a carryover from percussion rifles, heavy leaf springs, and thick primer cups. John Browning demonstrated that the heavier hammers were not necessary, his 1878 design that became the Winchester 1885 High Wall had a much lighter hammer, and dominated target shooting in the last decade of the 1800s, beating out the Sharps, Remingtons, Ballards, Wessons, and Marlin rifles.

The hammer doesn't store any energy so it can't be a source of energy - it simply transfers the energy stored in the spring. The equation above is one means of calculating that energy, but it doesn't imply the hammer's a source of energy. If we knew the spring constant, we could use a hammer-independent equation to calculate energy. And since energy's supplied by the spring, it's constant, no matter the mass of the hammer - decrease hammer mass by 20%, and hammer speed increases by 12%. Energy remains the same, but power increases 12%, while muzzle-jarring momentum and lock time decrease by 10%.

At any rate, my experience with revolvers has convinced me there are manifold benefits to a lighter hammer. There is a practical limit, though, and not knowing enough about AR15 design, I understand those hammers may already be closer to that limit. The basic idea (and physics) is the same, though.

[Tom68]

You see, the 100 lb brains did chime in

So, for all the physicists out there... exactly how is the energy in a spring measured? for that matter, what instruments are used to measure lock time, and dwell time? I know this is really deep laboratory stuff, but I do find this sort of information interesting.

[Brian Pfleuger]

The force exerted by a spring is expressed as:

F=-kx

where F is the force, x is how far it's stretched and k is the spring rate, or spring constant.

The potential energy of a spring looks suspiciously like the standard Kinetic Energy formula:

PE=1/2kx^2

Instruments to measure barrel time are pressure/vibration strain gauges. More information about strain gauge instruments, barrel time and links to barrel harmonics and the like can be found here:

http://www.shootingsoftware.com/pressure.htm