Chronograph accuracy

[John23]

Gday Everyone

After some mixed readings on chronographs over the years I have found myself wondering how much of a valuable tool they are?

I know using a rcbs unit my loads presented as slow comparatively to what appeared down range in Moa.
I appreciate that a higher than advertised BC rating could give similar symptoms although I don't believe many manufacturers under rate their pills BC rating .

Using a f1 chronograph I have whitnessed variable speeds on different occasions .

Last time using a F1 I was third in line with some mates shooting .

First was a 223 and had consistent and realistic readings.
Second was a 300 black out that once again had realistic feedback from the chronograph.
3rd was myself testing some 175gr loads though a 308win.
I recorded 4000-4015fps consistently over 5 shots....

This day with the 3 rifles being used has caused me my lack in faith.
The conditions were for the most part identical and over the time span of 20mins.
This for me eliminated light /temp conditions as a major factor to the readings.
The F1 was set up at 2-2.5m from the muzzle .



Talking to another bloke that told me he was getting 2800fls
Out of a 243win with 75gr pills....

These numbers are all over the bloody shop!

This leaves me with some questions

Are there good and bad chronographs?
Have people tested multiple chronographs side by side comparatively?
What are the perfect environmental conditions to use these tools?
What is the best distance to set these tools up from the muzzle ?
Can the data be believed and are chronographs worth owning?


I am considering giving the magnaspeed ago.
I like the fact it strays away from the standard way of measurement .
What I don't like is the fact you are essentially fitting a tuner/barrel weight.
The way i interpret this is the shooter must find a accurate load and then fitt the magnaspeed to test for speed and divinations?

It's a method of load development i have never tried although the ladder test would be the only reliable way to see what's going on?
Only problem with this method is environmental is a uncontrollable factor .

Until my current and now retired 308win barrel (which is all vertical) I have found my best groups make a nice flat water line on the target .

Then to make my brain hurt more is having the benchrest shooter at Silverdale tell me I am wasting my time weighing each charge .

How do I reliability measure speed and divination ?
Or do I even bother ?

After reading the es sd thread I was left wondering how much of the data was accurate to begin with ?

[Norm]

I have tried a number of different chronographs and now use the Magnetospeed which I find better.
They all have an error factor that you need to consider when considering ES/SD numbers.

The only "accurate" chronograph I know of is worth over $200,000. Here it is in use in its purpose built 25m indoor range.

[Barry Davies]

Ask 5 different people and you will get 5 different answers.
Chronographs are no different to any piece of equipment --you get what you pay for, less a bit for profit.
4000f/s? I doubt it by at least 1000f/s.
Personally I use an Oehler 35 which I have had for many years ( cannot remember exactly when I purchased it ) at least 15 anyway. Never had any problems with it that were not my own fault.
However bright sunlight is a killer even with the skyscreens. No question it operates with acceptable consistency in overcast conditions.
Electrical interference from other instruments _ phones, Radios etc , will upset it. Not to mention transmissions from the nearby airport. ( Bendigo )
Those problems, once aware, are not insurmountable.
Set up is with the first screen 3m from the muzzle --prevents muzzle blast from giving you false readings.
I believe 2 ft between screens is not enough unless the processor is such to cope with it. I set mine at 6ft and have used it at 10 ft between screens.
I find it useful for speed only, but if you fire enough rounds to be meaningful you can glean something from the SD.
I have tried many times to relate the shot position on the target with the chronograph reading --usually does not work but might mean something if the rifle was tuned properly.
If you want to play with variations in load, seating depth, primers etc at various temperatures, then its a handy tool --assuming it's accurate? ( Proportional to cost )
You are definately NOT wasting your time weighing each load, in fact if you don't weigh each load then you ARE wasting your time. With all due respects to the BR shooter.
You can get by without a chronograph but they do make life easier and shorten the distance to achieving a properly tuned rifle.

[John23]

Norm!!!

Can I just borrow that chronny for the weekend?
I will bring the box trailer up and grab it!


Mr Davies

Yes 4000fps is about 1200fps more than what the old girl is doing.

I had not considered interference as factor although on the day of my extreme 4000fps reading we were out in the bush and far away from any electrical , cellular, radio ect.

Light pollution was a known problem to me.
Excuse my ignorance these chronographs have a inferred? ultraviolet? beam that is broken correct?
If so would a chronograph work best at night time?

I will look at the Oehler 35, they look like a good design with the third sensor and extra length.
I assume it is within the program that you can specify the distance between each sensor ?


JH

[macguru]

Yes, I weigh each load with a digital that does not wander with respect to its zero. most shots are within 5 fps of the mean value so its working.

Just for fun, here is a pic of someone's chono running a 22-284 with light pills. I believe it, but you may never see these figures personally

[Barry Davies]

Don't believe that the Oehler uses either IR or UV to detect projectile, rather it " sees " the black form pass against the overhead light.
The model 35 that I use has only two skyscreens where the 35P is equipped with 3 plus a printout.
The 35P has a max spacing of 15 ft and the centre screen must be centrally located ( within 1/4 " ) of the two extreme screens.
They will not work at night ( without light ) and are particularly sensitive to existing light conditions.
The 35 has an internal adjustment for setting the distance between screens, I guess the 35P has something similar.
The 35 is of course obsolete, superseded by the 35P
Set up is important so I use a bore fitted laser to align both screens. The whole thing works to my satisfaction. Repeatability is proven over time. As far as accuracy of readings is concerned -- well how do you check it, on any chronograph?
Using ballistic programs is a reasonable enough check of speed against projectile drop = a certain MOA. Not so much at short ranges but certainly over the longs ( 900+ )

[Norm]

John, I think you would need more than a 6x4 box trailer...... LOL

But I do think an organisation with plenty of cash like the QRA, could build an accurate purpose built chronograph facility. Then hire it out to its members.

[John23]

All good Norm I got the 8x4 high sides.


Sydney Olympic shooting center has some nice tunnels with multiple chronographs over the distance .
Unfortunately it's only a rimfire / pistol range .

[johnk]

Tell me, why do you want to check velocities accurately when you have energy limits on so many ranges?

[John23]

I don't really understand your question JohnK?

[johnk]

OK. As QRA CRO, I am obliged to advise the various range users on how to apply the 3500 foot pound energy limit that applies to all Queensland ranges under the management of the Queensland Police Service WLB with distances over, as I understand, 700 yards/metres. An obvious answer would be to use a certified chronograph, but because such a device is not available to us I have leeway to suggest less finite methods.

Build & certify one & I will use it.

[RDavies]

OK. As QRA CRO, I am obliged to advise the various range users on how to apply the 3500 foot pound energy limit that applies to all Queensland ranges under the management of the Queensland Police Service WLB with distances over, as I understand, 700 yards/metres. An obvious answer would be to use a certified chronograph, but because such a device is not available to us I have leeway to suggest less finite methods.

Build & certify one & I will use it.

I think the best use of a chronograph is to check loads to make sure you have a small ES/SD, and to make sure you are UP TO a velocity range, not so much to make sure we are under a limit. I think with the cartridges/calibres in fashion at the moment that staying under energy limits is not a problem.

[bartman007]

+1 for Rod's comments.

I too use my Chrony to see that I'm running in the speed zone that I want for a particular projie/chamber combination. e.g. 180's running at approx 2950fps

I also look to see what ES/SD I have too, so some repeatability in readings is important too.

[AlanF]

My current thoughts on chronos : Magnetospeed if used correctly seems to be the most useful, because it remains stable regardless of location, lighting conditions etc. So even if its shot to shot precision isn't quite up to the ones with a longer base between sensors, it is a good way of comparing velocities at different times. Also good is its ease of setup. The main thing against the MS is that it adds weight to your barrel so will affect your tune. However for tuning, you can use a skyscreen type and directly compare it with the MS before and after. I'd be interested to hear more reports on Labradar.

[johnk]

... and it doesn't work with a Shadetree tuner (see last product on the page): http://www.shadetreeea.com/products.htm