Chronographs - How do you know theyre accurate?

[flyingfisherman]

Well, watched the art of precision rifle while it was on youtube and extracted some useful things from it.. One part talked about validating drop data. He (the guru) was saying that you cant beat using real world data because theres some factual data opposed to using hypothetical or bastardised data. He discusses altering the BC in your calculator to validate your trajectory. This is all good and well and i think he mentions this problem, but which do you think is more accurate.. the manufacturers quoted BC or my chrony? Well, i have to say i think the BC is probably more accurate than my chrony.

 

I have had the opportunity to run rounds through two chronies and received differing results by a few hundred fps. Are there any ways of getting calibrated chronographs without running into hundreds and hundreds of £s? I know that people are divided in either changing the BC to achieve the real world drops in the calculator or changing the velocity.. I personally change the velocity..

 

 

If i end up making an educated 'guess' with velocity in my calculator, what the point in using a chronograph at all? whos to say that it is consistent and can therefore be used to look at ES/SD?

 

Im not in a financial or mental position to go out and spend excessive amounts of money on a scientific chronograph but find it a bit of a joke that we go to the Nth degree with loading techniques to then measure the speed with potentially a yardstick!

 

Your probably getting the gist i have no confidence in my chronograph!

[tony]

Good question mate, I too have often thought how accurate these chronographs are, I have the same thoughts as you mate.

Tony.

[DaveT]

Ditto all that has been said BUT..... you have to work with something and the Chrono at least gets you somewhere handy.... real-world observed drops should obviously be recorded and used but a Chrono gets you close enough to dial in 'more or less' accurate elevation so as not to waste large amounts of ammo at extended range wondering where the bullet went whilst you compile your actual drop tables!

 

I also wish that I KNEW mine was accurate (CED Millenium)... i wonder what a truly calibrated one would cost!!!

[brown dog]

Whenever you hear someone saying 'field data is better than any ballistic program' just smile; they're actually telling you that they don't understand ballistic prediction

 

Which is better -Field Data or a Ballistic Program?

 

G7

 

 

One solid set of field data; properly modelled using a decent ballistic program that is then used properly will put you on in all conditions. The only thing it can't account for is an unseen environmental change or shooter inconsistency.

 

No point in shooters chasing an MV 'Holy Grail' until they accept that

 

 

The 'truing' shown in the video is a step in the right direction; but don't lose sight of the fact that it's simplified and shown to be 'zero defect' for 2 reasons: 1. it's entertainment 2. the fellow is trying to get you to buy the software (ie it's marketing). BC fudging alone will not give you accurate prediction at all ranges. As with all these things: SISO

 

Your chrono will likely get you within 10% of truth; that's probably a better start point for 'truing' a ballistic program than a total Wild-Assed-Guess.

 

But if people are then going to fall back on "only fired field data works" .....why bother?!!

[achosenman]

I agree with BD. I typed this as BD was posting so I apologise for any duplication …I can’t be doing with editing it now.

 

IMHO I think it’s a little bit more complex than an inaccurate chrony.

Do you believe the manufacturers’ quoted BC? (It is nothing more than a sales pitch) How did they measure it? Is the quoted BC relevant to the bullet shape? What is that particular bullet doing when it exits your barrel that affects drag?

 

Below is an extract from the help files of the ballistic program I use. These are the different drag models it uses.

 

Army BRL, Aberdeen Proving Ground.

(smoothed by the BRL and adjusted to fit firing tests)

G1.1 -S.A.A.M.I Standard model, Flat Based with 2 caliber (blunt) nose ogive

G5.1 -For Moderate (or low base) Boat Tails -7° 30' Tail Taper with 6.19 caliber tangent nose ogive

G6.1 -For flat based "Spire Point" type bullets -6 .09 caliber secant nose ogive

G7.1 -For "VLD" type Boat Tails -long 7° 30' Tail Taper with 10 caliber tangent nose ogive

G8.1 -Flat base with similar nose design to G7 -used for the US M2 152 gr .30 cal bullet, close to G6

 

S.A.A.M.I. /Remington Arms

(Smoothed and expanded)

RA4 -For 22 Long Rifle, identical to G1 below 1400 fps

From Winchester-Western (adjusted by linear equation)

GL -Traditional model used for blunt nosed exposed lead bullets, identical to G1 below 1400 fps

Other

GI -Converted from the original Ingalls tables

 

IMHO the ballistic subject is very complex and we cannot simplify it for convenience and then expect to get pin point accurate drop charts.

 

FWIW I try to get the BC for every load I use by testing over the chrony at known ranges. This is by far the most accurate method I can achieve with my equipment. The drag model I pick will still be a best guess so it will still have some errors. But the drop charts are pretty good. The BC’s for the loads are nothing like those claimed by the manufacture, but they are real and you don’t need to fudge anything for the kind of shooting we do out to significant ranges.

 

ATB

[flyingfisherman]

Some interesting theories...

 

Im intrigued by the physics and how to manipulate the trajectory.. ie are there any specific inputs which either change the shape of the trajectory (flatter or more of an arc) and also the total overall drop. Most people i speak to havent got a scooby doo of how to manipulate your BC or Velocity.

 

I went out and took as much environmental data that was required, went and shot out to 600yds and then made that match my ballistics prog. I do then need to alter the environmentals if i shoot elsewhere or in very different weather scenarios. Either way, it works for me..

 

achosenman - I concur with your thoughts about manufacturers sale pitches and find it difficult to believe that a Nosler BT has the same BC as a VLD in the same calibre and weight but thats what they say. What conclusion ive drawn from this at a reasonable range (700yds) that all things being equal, just different bullets, both have the same amount of drop..

 

How do you know that the BC isnt accurate and its your chronograph thats out?

 

 

BD - Can i conclude that ideally i should go out and measure environmentals accurately, enter the advertised BC and the velocity from a chronograph and alter one of them until they match? Which one would you alter and why? Also, does both BC and velocity have the same effect on the trajectory in relation to the arc and overall drop?

 

I wish i had a 1000yd facility on my doorstep!!

[achosenman]

How do you know that the BC isnt accurate and its your chronograph thats out?

That’s easy…I use two chronographs and a big disparity will show a problem. Since they both agree, I make the decision that they are correct.

 

Nosler BT has the same BC as a VLD

I haven’t looked, but the Nosler conundrum will probably be that they quote a G1 BC while Berger quotes a G7 BC.

Example. A 224cal 90gn VLD has a G7 BC of .281; the G1 BC for the same bullet is .551

 

The numbers will work if you input the correct data and use the correct drag model. Enter the environmental data and BC for the bullet in use. Don’t expect the drag model for a flat base bullet (G1) to work for a boat tailed bullet at longer ranges. If your ballistic program will not allow you to select the correct drag model, IMHO you are wasting your time…get another program.

 

I check the results by looking at the predicted velocity at say 200m. I want to see predicted velocity at what I see across the chrony. When I engage a target at range, the bullet drop is correct, but I cannot expect to use a drop chart at long range without accurate environmental data. Don’t work up a chart in dry cold conditions and expect it to work in a hot high and humid environment. If all the data you can enter has been sorted, the model will be more right than wrong.

 

ATB

[baldie]

Buy yourself an Oehler chronograph. They have a third screen that basically electronically verifies what the other two say....in effect, a default screen .

Acnowledged as the most accurate chrono made.

[achosenman]

Ronny IMHO the trajectory validation function is merely tacit acknowledgement that their drag model is wrong and they know it.

 

What BC are you using for what bullet, and which drag model are you running?

 

Are you using station pressure or barometric pressure?

 

baldie is absolutely correct IMO; the Oehler is the best out there.

 

ATB

[Missed]

I have to say that having crono data is an improvement over thirty years ago when we had to rely on manufacturers information.

 

I also think that folks are getting too tied up with published figures. It is my understanding that both the BC number and the G numbers are averages taken over the 'useful range' of a given bullet. The BC of a bullet will change in relation to its velocity and therefore by default will be open to some variation. If you want to work out the BC of your pet bullet, take two cronos a set distance apart (1000M?) and lob some rounds through both screens. Failing that you you may use manufactures who use doppler radar info (Lapua).

 

As a matter of interest, I have used LB for my come ups for quite some time and I have to say it has been pretty well on the money out to 1400m.

[brown dog]

Some interesting theories...

 

Im intrigued by the physics and how to manipulate the trajectory.. ie are there any specific inputs which either change the shape of the trajectory (flatter or more of an arc) and also the total overall drop. Most people i speak to havent got a scooby doo of how to manipulate your BC or Velocity.

 

I went out and took as much environmental data that was required, went and shot out to 600yds and then made that match my ballistics prog. I do then need to alter the environmentals if i shoot elsewhere or in very different weather scenarios. Either way, it works for me..

 

achosenman - I concur with your thoughts about manufacturers sale pitches and find it difficult to believe that a Nosler BT has the same BC as a VLD in the same calibre and weight but thats what they say. What conclusion ive drawn from this at a reasonable range (700yds) that all things being equal, just different bullets, both have the same amount of drop..

 

How do you know that the BC isnt accurate and its your chronograph thats out?

 

 

BD - Can i conclude that ideally i should go out and measure environmentals accurately, enter the advertised BC and the velocity from a chronograph and alter one of them until they match? Which one would you alter and why? Also, does both BC and velocity have the same effect on the trajectory in relation to the arc and overall drop?

 

I wish i had a 1000yd facility on my doorstep!!

 

Truing is more involved than just manipulating one value (that's my point re-the video chap).

 

I'm afraid I don't know what's adjustable on each program type sold and what can and can't be done on a particular 'brand'. I never look at them.

 

I'm a huge advocate of cards; get the thing modelled properly once and then concentrate on hitting; instant data, both hands on the rifle and not faffing with a little pda or phone in the field.....reading some of the things on the forum I'd guess that people virtually collect PDA and phone based programs, fanny about with them at home, then fanny about with them while shooting but never get them on and then buy another to see if that'll work.

 

Have a read of this; I'll do them for imperial scopes one of these days (work half done) http://ukvarminting.com/forums/index.php?showtopic=15139

 

 

MV and BC are the obvious tweaks, but as I think you realise, just changing the BC value and/or MV doesn't change the 'shape of the arc' you need to also identify and manipulate the value or values that change that shape until it matches reality.

 

I'd recommend a thorough read of Lindy's article linked within one of my earlier links; he describes the sources of elevation error in prediction pretty well.

 

 

@ Ronny: You're talking in a circle. At the top of the thread you're 'field data only'. Now you seem to be 'validation is fantastic'. Don't know what you're actually asking; but the morphing of your opinion to match what's correct would make a good analogy of trajectory truing.

[c18rch]

Get you BC from the applied ballistics book by Bryn Litz. These are measured by radar down ranges so will be the most accurate available.

 

As for chronographs, last time me and Oaken were at the range I fired 20 rounds over my chrony and 20 over his and there was a 30fps difference on average between the two. So no, you can't be sure they're accurate. After all, I bet no one has them calibrated after they've bought them.

 

As has been said you can't beat modelling from real world data.

 

Rich

[brown dog]

Get you BC from the applied ballistics book by Bryn Litz. These are measured by radar down ranges so will be the most accurate available.

 

100% agree with using Litz values sub-500 or 600m; but G7 is still an approximation, and it tends to wander away from reality further out.

 

His data isn't radar based though, he gets it from firing over 2 chronos ( 2 super-duper chronos!) one up range, one down range and he calculates his BCs from velocity loss over a fixed distance.

 

I would say that sub-600m his BCs give you data that, for all intents and purposes, is as good as radar.

 

Use Litz values and then you have BC nailed as one one value not to fudge.

[achosenman]

 

As for chronographs, last time me and Oaken were at the range I fired 20 rounds over my chrony and 20 over his and there was a 30fps difference on average between the two. So no, you can't be sure they're accurate. After all, I bet no one has them calibrated after they've bought them.

 

 

Rich

 

Assuming a MV of 3000fps thats still only a 1% error and that assumes identical test conditions for each string. For me that is still an order of magnitude more accurate than any other data we as shooters can obtain from another source.

 

FWIW the following is an extract form the CED users manual.

 

ERROR Warning system - The CED Millennium Chronograph is designed with an

advanced error warning system that provides the User with an indication when a

velocity (data entry) is received by the Chronograph that varies outside of the normal

expectation. In most situations, this fluctuation is a result of ammunition. Either faulty

loads or changes in components used. The ERROR indication allows the User to be

aware of the variance and to either edit, omit or accept the data entry as recorded.

Occasionally, environmental influences can and do effect the performance of a l photo electric sensors. Weather variations, lighting conditions, static electricity, bad

ammunition, or even muzzle blasts from nearby shooters, can effect the sensors. The

CED Millennium is designed to minimize these variables with the use of double

shielded cables, wide sturdy diffuser screens, and dual lens sensors. The "Error Warning System" is based on a calculated 7% margin. If a new data entry is + / - 7% of the average of the previously received data entries, a warning indication will occur.

 

ATB