Do you trust your chronograph


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atblis
October 26, 2009, 03:31 PM
Just wondering if you guys have any insight as to how accurate chronographs are.

Specifically, have you ever done a comparison, like line up three different chronographs, one after the other?

I am not entirely sure I trust mine. It definitely "shifts" after it has warmed up. But that's reasonable for electronics, digital scales are the same way.

I have one of these.
http://www.midwayusa.com/viewproduct/?productnumber=852429

Sometimes I wonder.

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Ed Harris
October 26, 2009, 03:42 PM
Normal industrial procedure is to fire a calibration check with reference ammunition on each setup to be sure that everything is working normally. I fire a few shots of Eley Tenex through my .22 rifle and if it is averaging 1080 +/- 15 f.p.s. sample average, as corrected for the ambient temperature, all is well.

Shoney
October 26, 2009, 03:47 PM
Some time ago, I thought my velocities were getting much higher than book data, yet showing no pressure signs at max loads. Since I didn't understand what was going on, I called the chrono factory.

The chrono company asked what elevation I was shooting at, because at higher elevations the air is less dense and higher velocities could be expected. Since I wasn't at high elevation, they told me to calibrate my chrono using high quality .22 LR, where the expected velocity is on the box (Federal 900B for example).

The quality ammo was to be fired out of a 24" bolt action or lever action .22, and should achieve the stated velocity within 50 fps or closely thereabout. The .22's usually vary less from the stated velocity than most commercial and handloaded centerfire cartridges. I was also told that the escaping gasses with unburned powder and residue particles of the cenerfire ammo crossing the chrono can give false high readings.

I run 10 shot strings of high quality 22 ammo across my chrono about twice a season, and that reasures me I am in a very good ball park!:)

ole farmerbuck
October 26, 2009, 03:49 PM
I have a Shooting Chrony Alpha Master Chronograph and my neighbor has about the same thing. We lined them up and got different readings. I dont remember what the numbers were though.

snuffy
October 26, 2009, 03:54 PM
Yes I do! Mines a Pact standard chrono, I've had it for 12 years. If I ever wonder if it's accurate, I run a few rem. standard velocity 22 rimfire rounds over it. IIRC those should be right at 1250 FPS., they usually are right on.

helg
October 26, 2009, 04:07 PM
I prefer not to rely on anything, even on forum advices, if I have not verified the claim myself.

My digital scale is accurate, and shows the same weight right after opening, and after a while, when it, like you said, "warms up". I have tested and verified this. I do understand how digital scale works. This helps me to get confidence in the scale.

Same with chrony. Before relying on its data, I used to conduct tests on it. Airsoft rifle with a simple homemade ballistic pendulum. Shooting at close distances, shooting aside of the sensors, or not straight over the sensors. Time stability of the device. A lot of things to play with. It adds some fun to the boring process of just punching targets.

Chrony relies on time measurement. Accuracy of the time measurement is far superior to the 4 digits that chrony gives you. Your watch does not drift when you wear it on your warm wrist or keep in a cold place. Non-straight shot is the first factor of discrepancy, straight cosine calculation gives a perfect estimate for that. Device vibration also can be estimated, but not that straight.

Muzzle flash, or sky, which is not clear, causes the device not to catch bullet at all, or to give unrealistic data. Different loads and guns distinct in the flashes, this may require some time to get confidence.

Try to make feel of your chrony, test it, and you can rely on it.

Asherdan
October 26, 2009, 04:08 PM
Specifically, have you ever done a comparison, like line up three different chronographs, one after the other?

Yes, kinda. Was out at the club one day and some other members had their chrony's out. I had my .22 bolt rifle and talked them into letting me put a couple of reference shots over each one, mine included. All shots came out within 30 fps or so of each other across the 2 shooting chronys and the one guy's Pact. I keep the (now <) 100 count box of ammo separate in the range box and fire a check shot or two before a chrony session, same as I was doing before and as the other posters have recommended. Having checked mine against a couple other chronographs does quiet the mind on the matter, though.

Steve C
October 26, 2009, 04:43 PM
I shoot some factory ammo, usually .22lr over mine to check readings and its always been at expected velocities. There are some things that can throw the readings off like any light flashes, powder passing over the chrono but in general the velocity reading appear accurate with few surprises.

The Bushmaster
October 26, 2009, 04:54 PM
Yes...I sure do trust my 20+ year old Pact 1 chronograph. It has never varied more then 30 to 50 fps (1160 to 1190 from a 20" barrel) when tested with CCI Mini-Mags.

~z
October 26, 2009, 05:45 PM
I trust mine, it's a Oehler P35. How could I not trust it?
~z

NCsmitty
October 26, 2009, 06:19 PM
IMO, many chronographs are setup too close and often get errors or erratic readings because of that. I setup at a minimum of 15ft. Obviously the folks shooting howitzers can benefit from the extra distance to the screens because muzzle blast and spewed aggregate can give errors and variations in the readout.


NCsmitty

qajaq59
October 26, 2009, 08:25 PM
If they are all so trustworthy, how come people keep shooting them? :evil:

Ol` Joe
October 26, 2009, 09:50 PM
I`ve both a Pact M1 and a old Shooting Chrony. I once taped the shooting chrony on top of the Pact screens and shot over both at the same time. The results were within ~2% max of each other. I feel this is fairly good accuracy from both units.

http://i34.photobucket.com/albums/d149/1Savage/DSC00911.jpg

1858
October 26, 2009, 10:16 PM
have you ever done a comparison, like line up three different chronographs, one after the other?


A couple of weeks ago I was using my chronograph and a friend showed up with his. After I'd finished shooting for the day, I let him use my rifle and my reloads and he shot five rounds over his chrono. I don't have the data in front of me but the average velocity that he got was close to the average I got but so what. Chronograph results are validated or corrected with field data.

You need to validate measured average velocities by shooting targets at known distances. Chronographs are good for load development, but you simply can't beat getting real data in the field. I've shot close to 250 rounds of the same 178gr .308 Win load at 25, 100, 150, 200, 300, 400 and 600 yards over the past two weekends and that gives me a much better idea as to the average muzzle velocity. Field validated MV will be more useful (and more accurate) to calculate comeups out to 1000 yards since the local range only goes out to 600 yards. If you have access to a ballistics program, you can make small changes to the MV until the calculated comeups match up with actual comeups. Density altitude is important too and you should know what temperature, elevation and barometer values to input to get the same DA value.

:)

ants
October 26, 2009, 11:29 PM
I trust it not to shoot me.





How many chronographs can say the same about us? :neener:

jbkebert
October 26, 2009, 11:36 PM
How many chronographs can say the same about us?

Not mine:D My chrono seems a little bitter with me since I stuck a arrow in it.

bluetopper
October 26, 2009, 11:45 PM
My chrony is bad about not displaying a reading at all.

I use it under an awning in the shade. Is this OK?

1SOW
October 26, 2009, 11:47 PM
ants +1

I started loading last year and borrowed a Chrony from a friend. I set it up carefully and it was a bright clear Texas day.

I wanted aload that gave my 124 gr FMJ 9mm a 130ish Power Factor (speed x weight / 1000). I was meticulous. I was shooting from a good rest through the Chrony at a 25 yd bullseye target. After trying three different loads I was right in the ballpark! (big grin here)

I later found competitive shooters who have their (same bullet) ammo checked regularly at major matches. Their load was NOT my load (similar guns/bbls). I had to be shooting light compared to their load. (big frown here)

I need another chronograph to compare with my last results. I upped my charge on faith---I know, I know.

I'm still trying to figure out how this is going to affect what chronograph I need to buy and how to check it. I need to be cost-effective as I don't load many variations.

1858
October 27, 2009, 12:09 AM
My chrony is bad about not displaying a reading at all.

I use it under an awning in the shade. Is this OK?

What sort of error messages are you getting? During my last session, the chronograph worked great when the sun was out and bright. Once the chronograph was in shade I started to get more errors. I probably should have removed the screens at that point but didn't. The sensors work off contrast i.e. a dark bullet moving across a light background. If the background is too dark, the sensor isn't going to detect enough of a difference and will give you errors.

:)

atblis
October 27, 2009, 12:26 AM
Also make sure the sensors are clean. That helps.

helg
October 27, 2009, 01:01 AM
My chrony is bad about not displaying a reading at all.

I use it under an awning in the shade. Is this OK?

Chrony works the best if it sees clear sky with no direct sunlight falling on its sensors. Mine does not work any good under a tree shade, ether directly under trees or under a tent that is not in a clear area. Light intensity fluctuates with the tree leaves in vicinity, and chrony can not set clear zero on brightness to catch its fluctuations from flying bullet. If your awning is away from tree shade, I believe that chrony should work. Just put its white screens on top to show to it dark bullet on the white screens instead of not-so-white ceiling.

Radaray
October 27, 2009, 03:37 PM
"If they are all so trustworthy, how come people keep shooting them?"

Hahahaha. That's the best quote I've seen on here. Very good question!

I believe the statement above is correct. They are useful for load development, as the readings should be construed as relative to what went before. Trying to achieve some manual stated velocity for a given load is not practical. They are extremely helpful when it shows a decrease in velocity with an increase in charge. This is a good indication that you have already reached your maximum load without reaching maximum pressure.

Read velocities are good enough to get you in the ball park for range adjustments, but nothing beats trial and error~~~unless you are a sniper.

helg
October 27, 2009, 04:09 PM
a decrease in velocity with an increase in charge. This is a good indication that you have already reached your maximum load without reaching maximum pressure.

I never heard about this. Does it mean that at some point muzzle speed decreases with increase of powder weight under a bullet? Are there any references explaining this?

snuffy
October 27, 2009, 04:52 PM
I never heard about this. Does it mean that at some point muzzle speed decreases with increase of powder weight under a bullet? Are there any references explaining this?

While not a reference, I just had that very thing happen here;

http://www.thehighroad.org/showthread.php?t=482323

It has to do with an extreme pressure spike caused by exceeding the normal expansion rate. A steady push is always better than a high peak then lower pressure. I've know about this for years, had it happen many times during wildcatting for handgun silhouette.

1858
October 27, 2009, 05:21 PM
Here's a comparison between the same load fired over two chronographs a couple of weeks ago with 2 hours elapsed between the first and second five-shot groups. The load consists of Lapua cases, CCI 200 primers, 168gr Nolser HPBT bullets and 43.5gr of Reloder 15. The weather changed considerably between the first and second groups (raining and cloudy vs. dry and sunny). Despite that, the average velocity of the second group is only 0.6% less than the average velocity of the first group.

(fps) (fps)
2768 2764
2766 2771
2783 2761
2777 2753
2793 2750

Avg. 2777 2760
ES 27 21
SD 10 8
Hi 2793 2771
Lo 2766 2750


:)

cm250
October 27, 2009, 07:09 PM
atblis,
Whats a good way to clean the sensors?

atblis
October 28, 2009, 08:24 AM
Same way you'd clean any other optic.
http://www.birdwatching.com/optics/cleaning_binoculars.html
Basically Windex and a non abrasive cloth. I've been using the microfiber towels recently.

1858
October 28, 2009, 03:56 PM
The light sensors in my Chrony Beta Master have plastic lenses so I wouldn't advise using any chemicals to clean them. A Q-tip moistened with water should suffice.

As for Windex or similar, I wouldn't use that on any of my scope or binocular lenses. Scopes and binoculars are coated and unless you know how ammonia reacts with the coatings it's best to play it safe and use photographic lens cleaning solution or similar ... that's what I use. I have a camera lens "puffer" (looks like a small rocket) that I use to blow dust off the lenses before cleaning.


From the link provided by atblis ...

Step 2
Moisten a Q-tip with water or lens cleaning solution and float off any remaining dust. Or if your binocular is waterproof, you can actually run it under the tap (but don't squirt it hard). DO NOT use fluid designed for cleaning eyeglasses or windows, as it may attack the coatings.

:)

JimKirk
October 28, 2009, 06:57 PM
About ten years ago two of my friends and I decided to compare chronographs as to how accurate they were. We starting out by shooting the same gun over each chrono and came up with around 100 fps difference. After talking about the results and knowing that each load can vary by 75 fps or more, we decided that the only way to test the chronos would be to set them up back to back to back. This way the variance would be limited to each round would be shown by each chrono not by three different rounds. The first friend had a reasonable(cheap) Chrony First model, the other had an Oehler 35(much$$) and I had a middle of the pack Pact Model 1. After setting the chronos as close as possible to each other and firring a round, we wrote down each recorded velocity. After fifteen rounds we averaged the total of the fifteen shots for each chrono. By using the average we found that there was only 33 fps difference between the three chronos. The Chrony was the lower number, the Oehler 35 was in the middle and my Pact I gave the higher number. So it boils down that each chrono was within 16.5 fps(within a few FPS) of the middle. The guy with the Chrony has since shot his dead center with a 270 Win, the Oehler guy has past away and nobody know where it is and I use mine every time I develope a new load for any of my guns. So yes I trust mine!

Jimmy K

4sooth
October 28, 2009, 09:09 PM
I once tested my bottom of the line Chrony against two Oehlers--one with the proof screens and one without. The extreme spread between the three was about 7 ft. per sec.

This was with factory .45 ACP and 9m handloads. I do like the Oehlers with the printer though. Very convenient.

rogn
October 29, 2009, 03:36 PM
One of the most accuate "standards " is a "springer air gun". The velocities from a good quality gun only vary a few fps per shot. Use the same pellet for each test. They donrt seem to vary much with temperatures either.

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