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Chronographing shotgun

Discussion in 'Shooting Related Threads' started by rrrocketman, May 10, 2009.

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  1. rrrocketman

    rrrocketman Member

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    I need the procedure for chrono'ing shotgun loads over my Oehlor 33. I've had this one for about 30 years and have run LOTS of rifle/pistol loads but nary a shotgun round. Anything in particular I need to know?

    Thank you,

    Rich Redovian
    Cody, WY
     
  2. Neil Winston

    Neil Winston Well-Known Member

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    Click above and read all about it, Rich.

    Neil
     
  3. shot410ga

    shot410ga Well-Known Member

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    Stand back six feet from the muzzle of the gun to the crono. You will be getting the speed from the first piece of shot. So, deduct about 15fps off the given speed. Average 10 shots, and you will get an accurate speed.
     
  4. BDodd

    BDodd TS Member

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    However, barrel length, chokes, temperature, all makes a difference in results off even your quality chronograph. While Neil Winston has far in away exceeded my work with chronographing shot loads (Oehler 35P), it is my current M.O. to test factory shells that I wish to replicate as described above and not worry about the fps results then test my reloads against numbers from the factory loads. This, of course, using my gun, it's barrel, and my usual choke for all tests If you want to brew up loads that are less or more fast, you can still use the factory loads as the beginning benchmark and never have to concern yourself with the truly actual velocities. Then, you could consider sending some of your favorite loads to a testing facility for actual results including internal pressure; I understand the folks at Down Range wads, (Kevin Lewis, Nebraska, 402.463.3415) can test loads for you. I can also recommend a personal chat with the folks at Oehler if you want some good info. breakemall....Bob Dodd
     
  5. samiam03

    samiam03 Member

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    When we Dyno a race engine we correct for temperature, humidity, barometric pressure, and altitude.

    Can you assume consistant results if you don't correct for those factors? For instance could you expect the same results a week apart?

    Is the dryness of the powder an issue as well? Does exposed powder in 90% humidity affect burn rate?

    Just curious

    sam
     
  6. samiam03

    samiam03 Member

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    Ok - couldn't wait for an answer and read the article linked above. I did notice that the article was written 10 years ago. Hopefully chronographs have become more feature rich since then. I'll have to do a bit more research to determine whether that’s true and if temp, humidity, biometrics and altitude correction is now built in.

    Still don't know how the t/h/b/a with the powder burn rate is affected by moisture content and how it would modify the results.

    Although I applaud the endeavor and reporting key factors (variables) were not included such as wind speed and direction and were the wind speed consistent throughout the tests. Additionally was there a measurable temperature increase effect in the trap house and in the field?

    Good starting point article.

    Now I'm off on a tangent - should stick to air/fuel ratios and the resulting boost pressures

    Sam
     
  7. shot410ga

    shot410ga Well-Known Member

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    Don't make a mountian out of a mole hill.
     
  8. Neil Winston

    Neil Winston Well-Known Member

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    Actually, samiam03, though C R Axtell always used a circular slide-rule when he corrected the dyno readings on my bikes, most of us chronograph users just keep all the stuff you mention in our heads and so don't need anything more "feature rich" than a bare readout or printout of speed.

    Our advantage is that most "corrections" are, as far as we know, very small. Since we are not dealing with ambient air (the shell gets its oxygen - and even its nitro boost - from inside) we are able to use zero for that correction and get away with it.

    Altitude probably has a effect but, again, since the source of the fire is internal, not atmospheric, it's restricted, probably to air drag and over 6 feet, and so can also be pretty-much ignored.

    Wind's pretty much the same. I doubt if a tailwind vs headwind can be detected, since shot-to-shot variability is far greater than a wind effect can be, hurricanes excluded, of course.


    Temperature is more complicated since not only do different powders react differently, so do different loadings of the same powder. We just remember things like this and apply informal corrections based on experience and today's temperature.

    <a href="http://photobucket.com" target="_blank">[​IMG]</a>

    <a href="http://photobucket.com" target="_blank">[​IMG]</a>

    As far as your concern about burn rate, it's not really applicable to shot speed. There are any number of "burn rates" which will produce a speed, after all, and even pressure with a single loading is only generally related to the speed of a particular shot, since as Nolte says, if the powder doesn't burn right now it will later.

    "Biometrics" have not been been addressed at all in chronographs, as far as I know, and we are all still waiting for this breakthrough.

    If I were to pick a "dyno-equivalent" for shotguns, it would be patterns, not chronographs. There temperature and altitude have a proven effect; humidity surely plays a role too at temperatures above, say, 80 or so, but again, shot-to-shot variability would make it hard to isolate. A chronograph is probably more like a Shore gauge - it tells you an important fact, based on a lot of variables, but in the end, you just use it as a number (or comparison.)

    Neil
     
  9. samiam03

    samiam03 Member

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    Thanks Neil

    I find this a very interesting subject. I now have a better understanding of the subject with your clarifications and the additional information you posted. The drop of of FPS at 0 degrees is as I expected.

    I also now realize the if the powder did have an elevated moisture content it would be converted to steam and contribute to the gas expansion.

    Invariably chronographs will become more feature rich as that's the competive nature of the developement and sale of scientific and diagnostic insturments.

    Now if I could tune to achieve 1250 fps I could beat them in the straight aways but handling the cornering might be a bit tough.

    I am extremely grateful for the time and knowledge that you've shared.

    Sam
     
  10. rrrocketman

    rrrocketman Member

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    THank you all very much! Great article Neil -- thanks!
     
  11. Neil Winston

    Neil Winston Well-Known Member

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    samiam03, as you guessed, there is progress in chronographs just as everywhere else. Here's the hottest new thing:

    <a href="http://photobucket.com" target="_blank">[​IMG]</a>

    From it you get

    1. Pressure, both as a dependent variable and a check on the main interest,

    2. Shot speed, as measured by industry-standard "coils." This is the real thing.

    The machine is an Oehler Model 84 and you won't find one at Wal-Mart.

    Neil
     
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