evaluating chronograph results


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Old 07-28-2008, 03:44 AM   #1
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Default evaluating chronograph results

What can you tell from a chronograph? Other than the speed in feet per second most chronies nowadays will also tell you the average, which can be the median, midpoint or mode, but in this case it will be the median. This is adding up all the velocities and deviding them by the number of shots. You will also get the extreme range which is the difference between the fastest and slowest shot. And lastly you will get the standard deviation which is the best evaluator of consistancy. I'll give an example with a load. Lets say this 40 caliber load had velocities between 964fps and 1018fps with an average of 970fps.These velocities were within range of those listed in the loading manual so I know my pressures are safe. If you load is much higher than those listed something is wrong and your pressure is too high!! Wrong powder, wrong charge, wrong bullet, old manual. Something is wrong and you should stop immediately before you end up in a unhappy place. Okay back to my load. We have and extreme spread of 54fps. Not bad but nothing to write home about. Maybe a primer wasn't seated quite right or I spilled some powder or something. I'm still in the ballpark and now I'll look ant the SD. In this case it was 13fps which is good. This means that 95% of my shots will be in between 13fps over my average of 970 fps to 13fps under of my 970 fps average. CD



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Old 07-30-2008, 11:12 PM   #2
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If you're working up a target load, velocity can be very important for accuracy over long distances. For self defense, or hunting there are many factors to consider, but it comes down to bullet performance in the real world. In the lab, on paper, or on the computer, a round may appear very impressive, but if it fails to perform in real meat in a real life and death situation, all of that theory doesn't mean much.


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Old 07-31-2008, 01:09 PM   #3
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You want your standard Deviations to be as low as possible. That being said pistol ammo is a different beast then rifle ammo. I know in my 45acp it tends to stay up there because of the amount of powder to the size of the case relationship. Once you get all your data and you figure out your average velocity and SD and ES (Extreme Spread) you can use the figures along with a ballistics calculator to make drop charts taylored to each load.

It will also well your load is perfroming. To a point, If your rifle is shooting 3" groups and your SD is 100 or 200 fps then you should look at your powder charging methods and seating depth.

That being said ( I love that phrase) I would not put too much stock in chrono readings because I have had some with SD numbers in the 50 and 60fps that shoot better than loads with much lower SD numbers. I have found too that some powders will outperform what the books say in terms of velocity. I had one load in my 223 with VV N133 that was clocking 200 fps faster than the mas load and it was a way below that load. That is a big help as well.

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Old 07-31-2008, 01:13 PM   #4
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You are correct Seedy ... but if all you are using your chrony for, is to try to match data out of the book, then you are falling short of the true potential of your chrony.

I use my chrony for all of the above of course, but my main objective when chronying a load is to tweak that load to fit my personal preferences and the preferences of the particular firearm I am loading for.

For one of my long range sticks I am looking for consistent results in terms of accuracy. Trying to find the fastest, hardest hitting load with a specific projectile that a particular stick will eat reliably and still punch sub 0.50 groups ...

For a pistol I am trying to do the same, but also trying to tweak it so that it meets all of the criterion as stated by pioneer461 above. And when it comes to my PD loads, I am going by feel as much as I am the data. How's the recoil? How's the accuracy? Then I take a close look at all of my chrony data, compare it to the book, etc.

One thing to always consider, especially where I live, is weather - and how it may affect results in terms of data. I live in South Carolina, a tropical environment for the most part where our average mean temperature year round is 74 degrees. We have temps in the eighties in November ... but when the sun is beating down on you, even in the winter down here, it can drastically change how your propellent performs as compared to the books, where most data is compilled in much colder states - even if it is indoors at times. So, all of that has to be taken into consideration.

Temp variances come into play for instance, if I am chronying a hunting load in September here in SC where temps regularly reach into the nineties in September ... but I am taking that load to hunt Elk in Montana in October or November where there may be subzero temps awaiting me when I step off the plane.

If I am shooting competition pistol and heavy plates, I have been known to leave rounds on the dash of my truck between runs to heat the propellent to the max before shooting ... especially on loads I ran during winter months or during the Spring. But I know how much I can get away with because I am familiar with the chrony results of that load and have grossly overeducated myself in advance using that chrony.

Something else I always, always take into consideration - and this comes from years of trial and error. Certain weapons, especially sidearms made by major manufacturers in Europe such as SIG and H&K, is that they are built to handle European specs, not SAMMI.

Then there is another consideration when using a chrony and that is, has your chrony been calibrated? If not, then you should only rely upon it for exactly what you already stated, relative velocity. And you use it, as you are working up a load, to see where an increase in charge offers no increase in velocity ... at which point you know that you are pushing pressure limits.

Now, a lot of people try to match chrony results of factory loads, with handloads. Bad idea.

You cannot safely match the velocity readings taken for commercially loaded ammunition because it is usually loaded with powders not sold to handloaders. Your powder may generate more pressure getting to the same velocity any given commercial load achieves. This is especially true of the Hornady Light Magnum line, for which not only the powder but the compressing method used to assemble these cartridges are proprietary and not available to handloaders. To reach the chrony results you see from their factory loads, you would have to grossly overcharge a handload and exceed some serious safety limits.

A chrony in the hands of someone who uses it as a tool, and as part of a process, is a good thing. But in the hands of the wrong person who does not have a complete understanding of the process - and a chrony can become an instrument of potential catastrophic failure - in your hand and face.

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Old 08-01-2008, 07:14 PM   #5
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When I finally picked up a new reloading manual I quickly noticed that the max loads were considerbably lower than the one that were listed in my old manuals. I had been using these loads for many years. I bought a chrony at that time to check my loads that I had accumulated over the years. I had a chrony years ago but a .177 pellet took out the readout screen. You guys are right, there is a lot more that a chronograph can tell you especially if you combine it with a ballistic program. Though I would like to competative target shoot or hunt large game I don't have the time. What I do have is couple of free hours everyday and the secluded area to go out and plink. I have been reading articles from guys like Rick Jamison for years and know there exists a much higher level. I do reload for a lot of calibers, especially pistol, and I would guess the only expertise I could claim is doing it on the cheap. CD

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Old 08-02-2008, 03:42 AM   #6
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Quote:
Originally Posted by seedy View Post
When I finally picked up a new reloading manual I quickly noticed that the max loads were considerbably lower than the one that were listed in my old manuals. I had been using these loads for many years. I bought a chrony at that time to check my loads that I had accumulated over the years. I had a chrony years ago but a .177 pellet took out the readout screen. You guys are right, there is a lot more that a chronograph can tell you especially if you combine it with a ballistic program. Though I would like to competative target shoot or hunt large game I don't have the time. What I do have is couple of free hours everyday and the secluded area to go out and plink. I have been reading articles from guys like Rick Jamison for years and know there exists a much higher level. I do reload for a lot of calibers, especially pistol, and I would guess the only expertise I could claim is doing it on the cheap. CD

You think these are lower than the last few manuals you should see some of the data my grandfather had worked up. Well within max and min loads 50+ years ago. We are talking WAY over max now I am talking 5 to 10 gr over max loads now. I think it is because the powder manufactures are getting much better at making powder or lawyers are getting better and pussifying america.
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Old 08-04-2008, 02:46 PM   #7
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Use your chronograph to determine the approximate velocity your loads deliver.

Analyze your targets to determine your best loads.

Bob Wright



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