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Cronograph Question

Discussion in 'Uncategorized Threads' started by Zuzax, Aug 25, 2008.

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  1. Zuzax

    Zuzax Member

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    When graphing a shotgun load does the cronograph read the long shot string differently than a bullet? Do I need to add or subtract from the reading or do anything different?

    Cheers,

    George
     
  2. BigM-Perazzi

    BigM-Perazzi Well-Known Member

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    Can't answer that, but, for reference, I usually shoot a factory shell or two and get a reference velocity since they state theirs on the box.
     
  3. Bob_K

    Bob_K Well-Known Member

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    Hobby chronographs read the first pellets over the screens. Commercial chronographs measure the center of mass of the shot string. Check out the Oehler Reasearch discussion on their shotshell specific chronograph.

    ...Bob_K...
     
  4. phirel

    phirel TS Member

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    George- A light chronograph will read the first shot that passes through the screens. The first shot is a little faster than the shot cloud mass.

    For me, the consistency of the recorded velocity of a load is more important than the actual velocity of the leading shot.

    Pat Ireland
     
  5. nipper

    nipper TS Member

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    oehler seems very high end any idea on cost??

    bill
     
  6. Neil Winston

    Neil Winston Well-Known Member

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    Bill, twelve grand will get you one after a bit of a wait. Figure another few thousand to set it up. It's high-end, as you say, but it's the only one which will answer some questions and if they are worth answering, so is the cost. My 71 gave up so that was the only choice for me.

    Neil
     
  7. Zuzax

    Zuzax Member

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    Thanks for the information guys, that helps.

    Cheers,

    George
     
  8. Neil Winston

    Neil Winston Well-Known Member

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    Zuzax, the above link will tell you perhaps more than you want to know. The specific answer to you question is that a light-operated chronograph starts a clock when enough pellets appear above it to make the clock start. It's more than one pellet that's for sure but how many more than one has never been answered as far as I know.

    If you use cylinder or skeet or IC chokes, you can can check not only the speed of your shells, but also their consistency. With tighter chokes your measured speed will be higher and consistency guesses will be suspect.

    Neil
     
  9. phirel

    phirel TS Member

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    Neil- I may have learned something from your last post. I had believed, for reasons I can't remember, that one shot (the first one) could be read by a light chronograph. Can you elaborate on why this is not true? What actually starts the clock on a light chronograph?

    Pat Ireland
     
  10. Neil Winston

    Neil Winston Well-Known Member

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    Pat, click on my chronograph report at the supplied link. Then look at the photo on page 3 of section 1, the setup I used with two 35P chronographs to measure the same shot - Prochronos and others can be used the same way and get about the same results.

    Then mouse over to section 2, page 4 and read "More about errors." With a cylinder choke the two chronos gave the same speed for a particular shot within about 4 fps (on the average) and so must have been reading about the same thing, which I take to be the bunch of shot which photos tell us result from cylinder chokes close to the muzzle.

    The same photos tell us that a full choke produces as longer "string" at that close distance. (These two effects are reversed at target distances, of course) And in this case, the two chronos _do not_ read the same, often differing by 20-plus fps. Yet the leading single shot's speed could hardly have changed much between the closely-spaced sensors. The most reasonable explanation is that the sensors are unequally sensitive to what starts their clocks. If they were both sensitive to one pellet, the readings would be equal. But they aren't equal. So they are not sensitive to one pellet.

    So now you are going to say "But one of them may be and the other not." This isn't true either, since in some cases chrono #1 reads faster, in other cases chrono #2, and there is no apparent pattern to these differences.

    Neil
     
  11. Zuzax

    Zuzax Member

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    Wow! That's a lot to digest. I'm just working up a good dove load for next weeks opener. I loaded 19.0 gr of 700X, CCI 209, clay buster wad under 1 1/8 oz 7 1/2s. 8 rounds through a PACT cronograph got an average of 1250 fps. They were all with in 25 fps of each other and the pattern on the board didn't have any holes in it either.
    I feel like what Pat said about the consistency so I'm going to go with it. Recoil out of my Super X 3 is pretty light as well.
    Again, thanks for all the great information, it's been a great help.

    Cheers,

    George
     
  12. phirel

    phirel TS Member

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    Neil- Once again you have destroyed one of my over simplistic concepts about the way things work. You keep making me think as you wreck my current dogma.

    I have always tried to reduce things into simple models. I guess this makes me a rather simple person.

    Pat Ireland
     
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