Chronograph distance?

Discussion in 'Long Range Hunting & Shooting' started by Glenn Tullius, Oct 17, 2019.


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  1. jrock

    jrock Well-Known Member

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    I put it as close as I can without getting the diffusers blown off. 8 to 10 feet usually works. On the chonoys, the vertical distance the bullet travels from the sensor matters. There is a small window which I think the instructions talk about. If you put the short legs in first, the brass part is at the correct elevation of the bullet path. Works much better when you are within in that window.
     
  2. BHP9

    BHP9 Well-Known Member

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    For the .338LM I used 16' (muzzle blast), for .308/30/06/.223/5.56 I use 12'.

    For handgun I use 8'.
     
  3. Glenn Tullius

    Glenn Tullius Member LRH Team Member

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    At 5' I blasted the diffusers with my 6.5 cm, so I moved to 8', and that works, thanks!
     
  4. Gater

    Gater Well-Known Member

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  5. Gater

    Gater Well-Known Member

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  6. Gater

    Gater Well-Known Member

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  7. Gater

    Gater Well-Known Member

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    My Caldwell calls for 10-15 feet from the muzzle
     
  8. skipglo

    skipglo Well-Known Member LRH Team Member

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    The book is only a close reference and not an exact science....far to many variables come into play....seating, elevation, humidity etc
     
  9. Sierra96

    Sierra96 New Member

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  10. wv270wsm

    wv270wsm Well-Known Member

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    I’ve set mine at 15 ever since the 7 mm stw up rooted it the first firing lol. As far as being below book speeds a lot of bullet manufacturers fudge the numbers in their favor . In my opinion. But they do generally use longer test barrels and it’s also a controlled environment.
    I’m not by no means knocking any of them but thats been my experience. I ask the same question back in March I believe it was . I’m roughly 200 FPS slower than what the Nosler book shows in my 7 mm08 and my barrel is 4 inches longer than what they have listed. As I was informed by I can’t remember who on here my barrel just maybe a slower barrel . And that’s not a bad thing. Considering it’s shooting well under moa consistently with little work
     
  11. fiftybmg

    fiftybmg Well-Known Member

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    This is normal.

    1. Load data is assembled by manufacturers with proof barrels, which are not the barrels we use on rifles.
    2. Velocity is affected by barrel length. If your barrel is shorter than that used in the load data, you will get lower velocity.
    3. Reloaders have found on occasion that they can never duplicate the powder manufacturers speed without exceeding the max powder charge.
     
  12. PApa Black

    PApa Black Well-Known Member

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    I had the same problem as Glen and used a friends Magneto Speed and the problem was solved! The Chrono buddy would give 50 to 75 FPS spread and the Magneto Speed 3 FPS! I'm sold on the Magneto Speed V3.
     
  13. crkckr

    crkckr Well-Known Member

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    I believe most of the ballistic programs (ok, I'm showing my age again... apps!) have a correction for distance from the muzzle to the chronograph. I know my old one did but then, it was also in basic, so I guess I'm dating myself again! Just Google 'corrected muzzle velocity chronograph to muzzle' and you'll get a laundry list of web sites, including LRH. Depending on your distance, that could be at least some of your "missing velocity."

    I don't think the book authors cheat outright but they do have their moments. Using custom guns (I always felt Nosler was really bad about that), longer than "usual" barrels, they might be able to inflate their numbers a little but remember, their data goes out to everyone to check and the number of chronograph's out there now tend to keep them pretty honest. Whenever you get data that is contrary to what's in the book, go back and look at what they used again. Magnum primers? 26 instead of your 22" barrel? Slightly different bullet? I don't remember them listing powder lots but even that could have an effect! Ballistics is part voodoo and part science, although if you dig deep enough and hard enough you can usually "science the doo" out of the voodoo! Plus the labs have actual shooting tunnels with good, steady lighting over their chronograph (well, Sierra does, they'll be glad to show you if you stop by their facility in Mexico, MO!) and don't deal with as many of the variables we amateurs do!

    Honestly, stopping by and getting the free tour at Sierra, which I do every time I go up there... it's fascinating and I learn new stuff every time I've gone. I don't know if others have tours but if so and you get the opportunity, take it! Personally, I could spend hours and hours in their shooting lab! Plus you get to buy "seconds" by the pound! It's like a treasure hunt as each bullet has to be weighed and perhaps trimmed (of lead or plastic), has a missing ballistic tip (what a hollow point! Plus they still usually feed just fine) or has some cosmetic flaw that has zero effect on the bullet. I've got about a dozen .22 cal, 40 gr. ballistic tip bullets with no lead core that weigh 14 grains each! They should probably hit 5000 fps with a bit of Bullseye under their little boat tails! Heh heh heh. No range but yee-haw! Back when Sierra was in in CA I lived right up the road a ways from them and we used to get mixed bullets by the pound at scrap lead prices! No more of that but even today I'm like a kid in candy store when I go there! The only thing that limits my 'enthusiasm' is my budget!
    Cheers,
    crkckr
     
  14. DFHarley19

    DFHarley19 Member

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