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Velocity Spreads?

 
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  #1  
Old 12-13-2009, 08:55 PM
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Velocity Spreads?

I was wondering for long range shooting out to 1,000 yards what is the largest amount of velocity spread between shots? I have a really accurate load for my 300 but I was going to chronograph it.
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Old 12-13-2009, 09:44 PM
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Re: Velocity Spreads?

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Originally Posted by ovastafford View Post
I was wondering for long range shooting out to 1,000 yards what is the largest amount of velocity spread between shots? I have a really accurate load for my 300 but I was going to chronograph it.
If you have a good chronograph look for single digit SDs and if you can't get that low
up to 15 SDs will work but the higher you go the shorter the range for acceptable
accuracy.

At shorter ranges the low SDs are not as important but at 1000 + yards it is very important.

To get an idea look on a good ballistic chart that goes to 1000 + yards and use 2 velocities
25 ft/sec apart and you will see the difference in drop and wind effect that 25 ft/sec has
and cut it in half and that is the biggest number you would want.

My best performing 1000 yard + rifles have had a SD of 3 or 4. but this does not come easy
careful loading is a must.

This is just my opinion and some may dissagree

J E CUSTOM
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Old 12-13-2009, 10:40 PM
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Re: Velocity Spreads?

I take chrony readings with a big grain of salt. I bought a chrony alpha this year and shot it back to back with an old prochrony and they varied anywhere from 5-50 fps. I put more stock in the actual verticle spreads on the targets. Chronies can be helpful, but unless you have a really good one (and how would you know if you do?), I figure them for plus or minus 50 fps. I have seen one read exactley the same reading for the first two shots and then 50 fps different on the third.

Mark
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Old 12-13-2009, 10:54 PM
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Re: Velocity Spreads?

So Im probably better off actually shooting at that range than relying on a chrony to tell me my load is accurate to that range correct?
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Old 12-13-2009, 11:14 PM
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Re: Velocity Spreads?

Quote:
Quote:
Originally Posted by ovastafford View Post
So Im probably better off actually shooting at that range than relying on a chrony to tell me my load is accurate to that range correct?
I would say that you can probably pick up trends from a chrony. I would hesitate to throw away or select a load on one outing over a chrony. If you shoot it on two or three different occasions under similar conditions and you are getting fairly consistant readings, then that's probably a reliable trend. If a cloud obscures the sun for part of your readings, they are likely to be off. This happens to me quite a lot.

So the bottom line IMO is, where are the bullets hitting?
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Old 12-14-2009, 12:14 AM
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Re: Velocity Spreads?

Take care with your personal definition of 'accuracy' as well.
For instance, you imply your load as accurate, but is it accurate at range(needed range)?
Is your load accurate,, or consistent?
Is it accurate under the conditions needed(like cold barrel, hot temps, off a bipod, etc)?

The only correlation I'm aware of between accuracy and consistency, amounts to how consistent my accuracy is(hope that makes sense). My accuracy is taken to field potential, single shots.
So I might count on 1/2moa of cold clean barrel accuracy, to 600yds, off a bipod, with a click card, within 70 to 100degs, using my Browing in 6br.
But I wouldn't bet on it hot barrel grouping much better at 100yds.
Doesn't matter. I kill woodchucks with it.

I agree completely about cheap chronos. One thing I've concluded is that the single biggest improvement to ES/SD is a quality chronograph. I find that the ES people think they have is usally not actually that bad. And that's why they often shoot better than ballistics would predict.
So I use an Oehler with 20ft screen spacing, and I spend a great deal of time using it with cold barrel load development.
If you can't get a good chrono, go with field performance(as mentioned).
You know what ES you need with a quick ballistic check. And you know what really matters by field testing.
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Old 12-14-2009, 12:46 AM
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Re: Velocity Spreads?

Thanks for the help guys. I dont have a chrony and I could probably borrow one but I think I will just go out and start out at 500. Work my way out and see how accuracy/ consistency is. Hopefully to 1,000 if it groups well enough at the shorter distances. Then see how my cold barrel consistency is. And correct me if Im wrong but velocity spread is represented in vertical climb/drop?
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