Velocity at 10ft from muzzle and at the muzzle

Discussion in 'Long Range Hunting & Shooting' started by YOTE, Aug 31, 2011.

  1. YOTE

    YOTE Member

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    Apr 27, 2011
    I was just wondering if there is a way to get an exact muzzle velocity using your readings that you get 10 or 15ft from the muzzle. I'm sure it is a very small difference but the little things are the difference between a kill and a miss at 1000. For instance if I'm 3000 fps at 10ft what is my true muzzle velocity with a 105gr 6mm berger bc of .532? Ive done some searches and havent turned up much so if someone could give me a good answer I would appreciate it.

    Thanks
    Nick
     
  2. budlight

    budlight Well-Known Member

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    What your asking does not matter. I chrono measure @ 20 feet to get a more realistic speed.


    Bullets don't have a static BC. It is dynamic (always changing) Some manufactures give the change in BC within velocity ranges. Example is a .560 BC at 2800 + FPS At 2400 FPS the BC is only .530 and at 2000 fps it is now only .500.


    So for a long shot you have to get an average BC because of the decreasing BC

    I think Sierra bullets lists velocity changes BC's for their bullets.


    I've often wondered about aerodynamic changes with a 6 groove barrel over a 3 groove. That is why range BC calculating with real life bullet drop actually shows true projectile BC. Some manufactures list highly overrated BC's for their VLD bullets just to make a sale and the bullets never live up to advertised BC in the field
     

  3. WildRose

    WildRose Well-Known Member

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    Since this answer fits so many questions you should just cut and save it to a document so you can cut and paste it in the future.

    Sure would save a lot of typing.gun)
     
  4. budlight

    budlight Well-Known Member

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    You did not answer his question! WildRose

    YOTE, You could search for a better explaination. But the jest of it is: You have to have a powder and load with minimal FPS variation. Lets just use your 3000 fps numbers. Zero in lets say 200 yards with the tinnest group possible right on the X. Next shoot groups at 300, 400, 500, 600 or what ever. Measure your true bullet drop at each of these ranges. With your ballistic calculator. Plug in all your correct information It really requires an air density altitude meter.

    Then you adjust the BC number up and down in the calculation tables to match the true flight of the bullet.

    I've toyed with the idea of using super thin target paper and putting out a row of 100 yard spaced targets. Then you could fire 3 shots and do the measuring all at once. Super thin is the problem because you don't want to slow down the bullet and artificaly as compared to air. Light beam targets that score the bullets point of entry would would be cool. Instant read outs right at the bench rest

    This is how to correctly be able to "dope the scope"
     
  5. WildRose

    WildRose Well-Known Member

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    You're right. I didn't answer it because your answer fit so well.

    Pardon me for giving you the compliment.
     
  6. rscott5028

    rscott5028 Well-Known Member

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    There are a lot of factors that affect the precision, accuracy, and repeatability of your chrony readings not to mention the ES/SD of your handloads.

    I doubt that the difference you're referring to is within that level of precision that you're able to measure.

    You could certainly do your own scientific testing to validate it. But, it will be a challenge.

    You can try backing into it by entering a higher value for MV above your actual measurement until the velocity at the chrony distance matches your measured reading.

    In any case, you'll want to verify your drops at long range and make sure that all of your inputs correspond to the actual POI at several longer distances.

    The more dope you gather, the higher your confidence will be.

    -- richard