Chronograph thoughts

Just wanted to see what people have to say about the various types of chrono available, I need to get the velocity data to setup my CDS dials so bought a Caldwell chrono and had some conflicting results which I think is partially due to user error but given the discrepancy it makes me wonder how accurate the data really would be even under ideal conditions.

So yesterday I set it up, overcast conditions which probably would've been perfect had I not fitted the sun shades. It reads about 2500fps
Today I do the same in sunny conditions, fit the sunshade however I'm pretty sure there was sunlight directly hitting the unit. It reads about 2600fps

A difference of 100fps just because of lighting conditions seems significant, so used correctly is the data reliable? is there anything I'm missing on top of that? is this style of chrono just garbage? lol

I have a Pro Chrono plus and a F1 Chrono. I find they can be sensitive to certain light conditions and overcast days are good for the best results. On sunny days the sun shades are a must. I have lined both mine up end on end so I could fire a shot and get a reading on both machines with the same bullet, results were about 20-30 fps difference.
What you can now do is do the shoot test. You can do drop charts for both the speeds you have got and then shoot at a target at say 400 yards and measure the inches drop and compare it with what the drop chart tells you it should be. If the actual drop is the same as say the 2600 fps drop chart inches drop you will be safe to say that speed was correct.

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Originally Posted by Mooseman

I have a Pro Chrono plus and a F1 Chrono. I find they can be sensitive to certain light conditions and overcast days are good for the best results. On sunny days the sun shades are a must. I have lined both mine up end on end so I could fire a shot and get a reading on both machines with the same bullet, results were about 20-30 fps difference.
What you can now do is do the shoot test. You can do drop charts for both the speeds you have got and then shoot at a target at say 400 yards and measure the inches drop and compare it with what the drop chart tells you it should be. If the actual drop is the same as say the 2600 fps drop chart inches drop you will be safe to say that speed was correct.

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Do you think 200 yards would be far enough? I don't have access to a range further than that but yeah sounds like a promising idea.

I have an old Prochrono (1990's era) and a Magnetospeed, the few shots I have fired using both were very close in velocity except one, which I'm pretty sure was due to the muzzle blast turning the Prochrono on a slight angle. I have had the odd really weird reading from the Prochrono, usually in bright sunshine coming from an angle.

A lot of the long range guys set the rifle/scope combo up using one fo the several decent chrony's on the market. Then go do some shooting to gain some data. And most do their verifying at 600 for speed. Then once thats sorted, they shoot at 800 to verify the BC. I wouldn't be shooting at 200 for verifying, just not far enough to give credible results.

Setting up your CDS dials is not a one day, shoot some boolits, type of exercise. The more boolits fired, in varying conditions, the more credible your dials will be. I've seen a client use a guides rifle that had a CDS dial supplied using sketchy data, supplied on purchase, not after some time. And at 500 metres, after a 2 hour wait, the client shot a bull tahr, dead as. Was a good time, lots of back slapping and smiles all around. On finally getting to the tahr it had been shot cleanly through the neck. BUT the client had been aiming centre mass, centre of the boiler room, had a good rest and bipod, had time to settle in to the shot. This wasn't his first rodeo, and that shot was a good 30 cm higher than he aimed and it all came down to shit data being supplied for the CDS dials.

Take your time, verify your data using lots of distance, and then order your CDS dials. The results will be worth it.

Chronis can be finicky, they need direct sunlight for bewt results. That is sunlight shining straight down on the top of them. The sun shades seem to make a difference on mine (Prochrono Digital) as in it works better with them on regardless of the weather.

When you set up the chronograph, did you have it set up exactly the same distance from the end of your barrel each time? They need to be set up a minimum distance from the muzzle, mine is 5 to 15 feet.

Did you shoot at the same time of day? Different light levels and angles affect the reading, ideal is middle of the day when the sun is at its peak.

As @Mooseman has said, next is the shoot test also called validation. Use the speeds you got and punch them into a ballistics calculator and see if it matches up. If you only have 200 yards then that'll have to do. Can you think of any public land nearby where you can shoot at a slip at a further distance? Validating the speed is key before you send away for your cds turret.

Chronographs will get you in the ballpark, testing the data is key.

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Originally Posted by Rated M for Magnum

Chronis can be finicky, they need direct sunlight for bewt results. That is sunlight shining straight down on the top of them. The sun shades seem to make a difference on mine (Prochrono Digital) as in it works better with them on regardless of the weather.

When you set up the chronograph, did you have it set up exactly the same distance from the end of your barrel each time? They need to be set up a minimum distance from the muzzle, mine is 5 to 15 feet.

Did you shoot at the same time of day? Different light levels and angles affect the reading, ideal is middle of the day when the sun is at its peak.

As @Mooseman has said, next is the shoot test also called validation. Use the speeds you got and punch them into a ballistics calculator and see if it matches up. If you only have 200 yards then that'll have to do. Can you think of any public land nearby where you can shoot at a slip at a further distance? Validating the speed is key before you send away for your cds turret.

Chronographs will get you in the ballpark, testing the data is key.

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Nah was different time of day also so that probably added to it all, roughly the same distance but I didn't measure it. First thing that comes to mind is Seddon rifle range, that goes out to 1000 yards but I'm not sure what the rules are in regards to shooting there or getting access, no idea about doc land. Odds are there's probably somewhere but I don't know about it haha

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Originally Posted by ElDax

Do you think 200 yards would be far enough? I don't have access to a range further than that but yeah sounds like a promising idea.

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Further is better you could try at 200 but I don't think you will see much in it unlike at 400 yards you will see maybe 20 inches drop, by the way what caliber are you shooting?

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Originally Posted by Mooseman

Further is better you could try at 200 but I don't think you will see much in it unlike at 400 yards you will see maybe 20 inches drop, by the way what caliber are you shooting?

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6.5 Creedmoor

Ive seen it done completly differently.....
zero at your normal 2-3" high at hundy..mark dial with nail varnish

go out to say 400 yards,dial what you THINK you will need,shoot group...adjust till its zeroed..then mark dial

keep going to what ever range you will shoot to...your dial will have 3-4-5 coloured marks now on it...... or a dope card with how many clicks for what range.

If you want consistency from your optical chrono you could build a light box with battery powered lights over the reading slits of the chrono. Atmospheric conditions will no longer be a problem, creating inconsistent results.

Here is the link to the thread with the photos:
https://www.nzhuntingandshooting.co....52/index2.html

Another chrony setup issue that many overlook is levelling and direction. The horizontal line over the photoelectric lenses needs to be the same parallel as the bullet path both in line front to back and left to right. If the setup is on any othet angle than dead in line then the distance the bullet travels from cront to rear sensor will change and in the microseconds measured the conversion to ft/ sec can vary markedly. So distance from muzzle, light factors And levelling are all imprtant to get consistent results.
Be mindful though that as othets have said, actual poi's per range are the best final proof of ballistic curves.
If your hunting shots are going to be under 400m then extreme precision is really not a big issue; just zero at 200-220 m and hold a little over as range increases :)

I had trouble with my pro chrony until I moved it out to 5 metres from the muzzle. The post of Woodys regarding leveling and alignment makes good sense too

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Originally Posted by Cigar

I have an old Prochrono (1990's era) and a Magnetospeed, the few shots I have fired using both were very close in velocity except one, which I'm pretty sure was due to the muzzle blast turning the Prochrono on a slight angle. I have had the odd really weird reading from the Prochrono, usually in bright sunshine coming from an angle.

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Yep, what Woody said is what I think caused my lower reading. The bullet has to travel a tiny bit further on an angle, so velocity will show as slower.