chronograph question

Most of us have a chronograph to test our reloads with....we also often use a set of check weights to confirm that our scales are properly calibrated.....

So, what do we use to ensure that our chronographs are properly calibrated?

Lastly, does a dramatic change of elevation effect the velocity of a projectile?
Will a load that makes major power factor at 6000 feet elevation go up, down or stay the same at say sea level?

Thanks to all!

Randy

Here is some info on velocity & altitude.

Ballistics: Altitude and Air Pressure within AccurateShooter.com

The only "easy" way I can think of to verify the accuracy of a chronograph would be to use a ballistics program. You know bullet weight, BC & drop. With that, the velocity can be calculated.

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I've had six chronographs in the last thirty-five + years and I regularly chronograph a lot of loads. The same loads have shown approximately the same readings regardless of the chronograph unit. I've used everything from the disposable Chrony to the Oehler 35P and the newer Labradar. If you're concerned about the accuracy of a unit, the Oehler 35P has the "proof" channel that helps to verify accuracy and isolate bad or questionable readings.

Readings with all chronographs will often vary from day to day depending on several factors, but the variances are seldom significant, 10-40 fps. I've seen greater variances, but not frequently.

I'm an authority on none of this, just reporting my observations.

There are numerous environmental factors which will change velocity - temperature, atmospheric pressure, and humidity to name a few. But those won't have much effect close to the muzzle, but will further downrange as they affect the bullet air drag.

The factories have ways of calibrating their chronographs, but I don't know of a good way for an amateur to do it. I just trust that mine is correct. I am generally more concerned with the standard deviation of MV rather than the average MV, so it doesn't bother me so much that I have no good way to check the accuracy of chrono reading.

I understand your question completely. As of now, there isn't any tool or method, or usable measurable constant to physically verify the chronograph readings.
The speed of sound is the only constant that 'could' be utilized in some way, where say an LED is placed above each eye and a loud wrap of something would trigger the LED's and the chronograph should read somewhere close to 1133 fps. That is just a theory I have, nothing I know of exists that could do this.
One thing I have observed with some chronographs, is if the unit or sensors are too close to the muzzle blast, anomalies show up that don't make sense. Moving away from the muzzle blast stops this.
Bottom line is, we have to know approximately what we should realistically be getting and we just have to trust what we are reading is good.
A lot of factors influence velocity.. That a whole separate discussion.

I've been reloading since the mid '70s. One of these days I'm going to try a chrony and see what the hubbub is about.

Skip the Chrony and buy the Competition Electronics $99 pro digital
instead. I've owned two Chronys and found them to be useless for
chronographing handgun rounds.

A chrony is nice to have to give you a "Ball Park" figure on your ammo.
As mentioned it can vary day to day by lots of factors and conditions,
so don't worry about a +/- 40fps in a pistol load.

You need not worry about how small your ES spread is also, since
I have had revolver/pistol loads that have had a ES over and
past the 100 mark and still get a tight group out of a powder.

I do believe that the more powder in a case, the better the chance
that the load will shoot better, with less powder flocculation.....

but that is just my findings in my weapons.

Yes, bullets go faster in "Thin Air", up here in Reno Nevada vs the Bay area.
When I moved from SF to Nevada, I found out that I could use the little .270 Cal, instead
of the BIG huge .30 caliber bullet, that I had been using for deer in California. (Grin)

You'll find that there is more operator error than unit error when it comes to the traditional chronographs. 2 major mistakes when using chronographs:

The chronograph is not level & held in place on something solid.
The shooter does not aim in the same place shot after shot.

The time of flight of the bullet is different when shot strait across the sky screens compared to if the bullet crosses the sky screens @ an angle.

I can't believe.....

...that anyone has yet come up with this answer to ensure your chronograph is calibrated.

Buy a box of factory ammo with the velocity clearly marked on it. Fire some rounds across your chronograph and see what the resulting average is.

I did just that when I suspected my chronographs readings were wrong. The ammo, Winchester 230 gn JHP advertised at 880 fps actually averaged close to 865 fps across my chronograph.

Thing about that is this. Although a box of factory ammo might be clearly marked as to velocity, that velocity is for their test equipment. You could fire a round of that ammo from 10 different guns and get 10 somewhat different velocities. Even guns of the same make and model could have enough variation as to cause velocity differences. Exact chamber size, throat, free bore, minor variations in the rifling, bore size . ETC ETC

Maybe I should have asked how the factory actually calibrates a unit?

Randy

Verifying your chronograph's accuracy -- or at least verifying that it hasn't gone batty since the last time you used it -- is easy. When you buy a new chronograph, also acquire a supply of test ammo. Calber and velocity don't matter, but all these rounds should be from the same lot and testing the ammo should always be done with the same gun .

Set up your chrono, fire 3 to 5 rounds of your test ammo, using your test gun, and record the average velocity. From that point on you have a "control" load and gun, and you use the same test before testing any new load to verify that your chrono is still in proper order. If, for instance, your test load averages 1250 fps in the initial testing, it should be right near that every subsequent time you run the test

Practically speaking, that's about all you can do to verify accuracy, unless you have access to a known, 100% guaranteed accurate chronograph with which you can compare yours -- and frankly I don't know where you're going to find one of those.

Kiwi cop said:

. . . Buy a box of factory ammo with the velocity clearly marked on it. Fire some rounds across your chronograph and see what the resulting average is.

Click to expand...

Factory ammo velocities are never OK for me. What was the barrel length used in their tests? What was the difference between the bullet diameter and the measured groove diameter? Barrel length can make a significant difference in velocities, so if you shoot a carbine and the factory uses a longer test barrel, it will appear your chronograph is not accurate.match what is stated on the box. Early Mauser 1898s, Krags, etc. with 30 " barrels and the ammo factory is using a 22" test barrels, how accurate will the printed box label be?

Second guessing properly set up chronographs is akin to not believing your compass. The most important piece of reloading equipment I own is my PACT. It measures everything I shoot across it. 22 Short to 22 LR, no problems. Keys are clean sensors, set it up properly and on a solid base, shoot level, follow instructions. I cannot tell you how many people shoot rifles across their chronograph that is 4 feet away from their muzzle and claim the equipment is junk, or don't bother to put on their sun screens, etc.

Companies that make chronograph equipment are trying their absolute best to assure accuracy. If you don't believe what you see on the screen, check the set-up. Trust your equipment or don't use it, but don't blame it.

Case in point for the benefit of using a chronograph was a trip to the range yesterday. I just bought a K38 Combat Masterpiece from 1951 and loaded up several different published rounds to test. One such load was just under a max load for a 148 grain HBWC. Published velocity using the powder company's online manual was 800 fps. Shot 2 rounds and the chronograph read over 1000 fps. Not wanting to shoot the rest of the loaded rounds, I went to empty the remaining 2 rounds and for some reason, the cylinder would not open. Had to take it home loaded ( thank god for my CCW). What I found was very troubling, a skirt had blown off the HBWC and lodged between the forcing cone of the barrel and the front of the cylinder. Another inch and the next shot would have caused quite a bit of commotion at the range at a minimum. Checked the loads after removing the bullets on the remaining rounds and found the exact right powder weights, so the rounds were properly loaded.

I have never taken a new loading recipe to the range without my chronograph and never will. Bottom line is trust your equipment, watch every shot result and be safe and secure with the knowledge gained.

growr said:

Most of us have a chronograph to test our reloads with....we also often use a set of check weights to confirm that our scales are properly calibrated.....

So, what do we use to ensure that our chronographs are properly calibrated?

Lastly, does a dramatic change of elevation effect the velocity of a projectile?
Will a load that makes major power factor at 6000 feet elevation go up, down or stay the same at say sea level?

Thanks to all!

Randy

Click to expand...

Oehler 35P with proof channel.

growr said:

Most of us have a chronograph to test our reloads with....we also often use a set of check weights to confirm that our scales are properly calibrated.....

So, what do we use to ensure that our chronographs are properly calibrated?

Lastly, does a dramatic change of elevation affect the velocity of a projectile?
Will a load that makes major power factor at 6000 feet elevation go up, down or stay the same at say sea level?

Thanks to all!

Randy

Click to expand...

Barrel length, barometric pressure, air temperature, different brand powder, bullet weight all can affect bullet velocity.

That and of course "not all chronographs agree"...

I gave up on "test" ammo, (factory) a long time ago. I found that factory ammo was far more variable than my handloads. One time I was testing 12 gauge, and my handloads would have a variation of about 15 fps, while the Winchester AA factory loads I was using as test loads had a variation of over 50 - 60 fps. I record all my reloads so I can duplicate the loads.

As with many of these threads, some prefer to complicate a process that is really pretty simple and straightforward. As I posted earlier, I've used six chronographs over many years. Time-proven loads have chronographed approximately the same velocity on most or all of the units but my notes aren't obsessively complete to the point I can provide exact figures. My records don't indicate which chronograph was used to record data.

In recording figures that approximately correspond using the various units over the years, I tend think they all provided accurate readings simply because the readings were very similar.

The factory load suggestion would be a good one except for a major drawback which renders the method worthless: the use of changeable factors, or "variables" as we frequently call them.

I’ve had some folks question the velocities that I’m getting with some cartridges....if fact, I questioned. So, I took other rifles and shot them using my chronograph. There was no parallel data! Some rifles shot slightly slower than expected.....some where a bit higher. The shot strings gave extreme spreads within reasonable expectations. Also, under similar temperatures, the individual rifle data can be repeated!

This doesn’t prove or disprove my chronograph accuracy....but does “tend” to support it’s accuracy. So, test firing other firearms with known (or seemingly so) velocities.....would be a good means of testing your chronograph. memtb

growr said:

Maybe I should have asked how the factory actually calibrates a unit?

Randy

Click to expand...

Now that has an answer. The timing circuit is calibrated against a known traceable standard, just like an electric watch. And is normally the LEAST of your worries in accurate, repeatable measurements of bullet speeds.
I recently "fixed" a chronograph with loose mounts, FILTHY lenses, and a loose battery wire. And as usual, the timing circuit was perfect. The only real problem was the loose nut behind the wheel who made no attempt to follow the manual directions on maintenance and operation..