Re: True muzzle velocity
The info below is from a Google search.
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There is a formula that will closely estimate this loss at normal chronograph distances:
You will need a scientific calculator to do the calculation. If you don't have one. Window's calculator will work. Click Start ~ All Programs ~ Accessories ~ Calculator to bring it up. Then click the "View" menu and select "Scientific".
On a scientific calculator, the "e" function is the inversion of "ln" (log number) function and that is activated by pushing "shift" or "inv" + the "ln" key.
Now:
Let CD = The Distance, in feet, from the muzzle to the center of the chronograph screens.
Let BC = The Ballistic Coefficient of the bullet.
Let CV = The average of the shot chronograph values.
Let MV = The Muzzle Velocity calculated from the Chronograph Velocity.
Then
e( CD / BC / 8816) x CV = MV
Here's how to do it.
CD = 7 feet.
BC = 0.300
CV = 1500 fps
On your calculator, enter the following, being sure to enter the parentheses "( )" characters in the equation. The (*) may also be entered as (X) on a hand held calculator and the "=" may be entered as "EXE" or "Calc"
"shift" + "ln" ( 7 / 0.3 / 8816 ) * 1500 =
This should return an answer of 1503.975 fps
Let's do my 280 Remington shooting a Hornady 139 gr. bullet with average chronograph values of 2818 fps
Chronograph distance is 15 feet.
Ballistic Coefficient of the Hornady Bullet is 0.392
e( 15 / 0.392 / 8816 ) x 2818 =
This returns a Muzzle Velocity of 2830 fps
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ss7mm
