Chronograph data

[Crunchy]

What should I do with chronograph data.  Do you average all rounds and use that as your standard, then use that data for trajectory info?

[thinkingman]

What should I do with chronograph data.  Do you average all rounds and use that as your standard, then use that data for trajectory info?

If you're calculating ballistics, then yes.
I look for the spread (deviation) to see how well I'm loading.

[Crunchy]

Is a spread around 50 acceptable?

[norsepeak]

little high, I like to see a max spread of 25, but that takes a lot of fine tuning.   You can use your average speed in calculating your drop data and developing drop charts, but keep in mind that it is only a starting baseline.  There are a ton of variables depending on what you plan on doing with the gun.  Air temps, powder temps, elevation....etc.

[jay.sharkbait]

Is a spread around 50 acceptable?

How far away was the target? And did you see any vertical stringing?

[bearpaw]

Is a spread around 50 acceptable?

I think that sounds high too.

[HUNT]

The spread may depend on how accurate your chronograph is also.  Some are better than others.   

[argie1891]

The spread may depend on how accurate your chronograph is also.  Some are better than others.

I will second the above my chrony is not anywhere as good as a pact I recently picked up. I hardly every got low extreme spread with it same loads on the pact are much better. I think the reason is the distance from the front and back electronic eye and a bigger window to shoot through. argie1891

[HUNT]

The most accurate chronograph for the general public is the Oehler 35P made by Oehler Research Inc.  It uses 3 screens instead of 2 to measure the speed.  The drawback is that they are spendy. 

Most accurate chronograph I have used, hands down.

[BULLBLASTER]

The oehler are very good chronos and have made a name for themselves. But if i were to buy a chrono right now it wouldnt be an oehler. I recently had the opportunity to use a magnetospeed and feel it is a better design than the oehler. It gives a true muzzle velocity (not 20 feet downrange) and doent rely on any light or light screens. It uses the magnetic field of the bullet.

Fwiw when I chronoed my load for my 300 rum out of 10 shots I had a standard deviation of 9. That's better than I was expecting.

[jay.sharkbait]

I'm just throwing this out here, but you really don't need a chronograph any more.

If you have a known distance and a fairly accurate BC you can get much better numbers using predictive algorithms.

[BULLBLASTER]

I'm just throwing this out here, but you really don't need a chronograph any more.

If you have a known distance and a fairly accurate BC you can get much better numbers using predictive algorithms.

How will you know if the bc is accurate without knowing the velocity? Also how will you know how consistent your load is? Velocity is a very important part of load development and data for long range shooting.

[jay.sharkbait]

I'm just throwing this out here, but you really don't need a chronograph any more.

If you have a known distance and a fairly accurate BC you can get much better numbers using predictive algorithms.

How will you know if the bc is accurate without knowing the velocity? Also how will you know how consistent your load is? Velocity is a very important part of load development and data for long range shooting.

The algorithm is key.

It's like celestial navigation. It doesn't tell you where you are. It tells you how far away you are from a designated point.

[Feanix]

Ballistics Coefficient is a product of velocity

[jay.sharkbait]

Ballistics Coefficient is a product of velocity

BC is a product of mass, diameter , surface area and surface condition.

[dontgetcrabs]

Ballistics Coefficient is a product of velocity

BC is a product of mass, diameter , surface area and surface condition.

Why does BC go down as velocity slows?

[Bob33]

Ballistic coefficients do change slightly as velocity changes.

[Feanix]

Ballistics Coefficient is a product of velocity

BC is a product of mass, diameter , surface area and surface condition.

Surface area and surface condition do not equate to drag coefficient. Drag coefficient is a product of velocity. Most bullet manufacturers use standardized drag models when calculating their stated BC and most are averages. I think only Sierra lists different BC's for different velocities, and not on all bullets.

Getting off track.
Crunchy: I use chrono data as a check for consistency in my loads (ES AND SD) and use the average velocity as a starting point for trajectory. A standard deviation of 50 is pretty high. Make sure you charges and seating depth (measured from the ogive) are consistent. When i was tuning the load for my 308 i kept getting fairly large SD's and ended up changing primers.

[argie1891]

chronograph data is at the very least a heck of a lot easier to get than doing the complex math you are talking about.. now some of us have a high school education and are not well versed past addition and subtraction with a calculator. for my money I will buy the chrono and you guys with sharp pencils can figure it out your way. and please do me a favor and don't come back with how simple it is to figure as an old man like me would never spend the time or energy to figure out what you are talking about. argie1891