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muzzle velocity vs chrono velocity

dandak1
Anybody know a formula to convert chrono velocity at 12' to actual muzzle velocity?? I know the loss isnt much and it is pretty meaningless in calculations, but I'd like to figure it out anyway.
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4 comments

Date Votes
  • COBmmcmss
    You would need a second chronograph, or you'd have to have all of the "dope" for the round (i.e. powder, bullet coefficient, etc.) Two chronographs spaced at precise distances is much simpler to calculate back to M.V.
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  • Tailgunner1954
    Not a formula, but if you input your BC and "muzzle velocity" into a ballistics program, and than look at the 340yd velocity. Subtract that from the MV and divide the result by 10 (or use the 20yd velocity difference and divide by 5). Add that number to your previous MV and you'll be fairly close to the actual number.

    The formula for the first 34yd is the same as the rest, just the sign is reversed (add the "loss" instead of subtracting)
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  • beantownshootah
    First of all, for any practical purpose the muzzle velocities at 0 and 4 yards are identical.

    I think Tailgunner probably has the most practical approach to estimate the velocity loss at 4 yards. (IE use a computer ballistics program to model/simulate it).

    This one will probably work fine. Just enter your parameters, and use 4 yard increments:

    http://www.handloads.com/calc/

    Edit: Sorry, this particular software only lets you input 5 yard increments, though for your purposes 5 yards is probably close enough. If you want a bit more accuracy you can decrease the 5 yard decrement by 20% to roughly model a 4 yard distance.

    For what its worth, using a typical match-type .308 rifle bullet with a muzzle velocity of 2800 fps and a ballistic coefficient of 0.45, you'd only expect a loss of about 8 fps at 4 yards.


    The problem with measuring the difference directly by placing the chronograph at 0 then 4 yards is the variation in MV BETWEEN shots is likely to exceed the decrement in muzzle velocity at only 4 yards.

    In other words, you wouldn't get a statistically significant basis to compare to unless you were to compare a good number of shots at the muzzle vs a good number of shots at your 4 yard distance.

    The better way would be to use two different chronographs simultaneously. . if you had access to two. . .though you'd have to make sure they were precisely calibrated.
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  • dandak1
    Excellent! this is exactly what I wanted. I read a long time ago there was a way to do it, I use the handloads.com calculator all the time...never thought of doing it the way it is presented though. Thanks guys!
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