McCall's Penetration Predictor
(simplified for desktop calculator)
This is just one portion of the penetration predictor that I worked up some time back from my own independent research (i.e. I ain't read it from no books.) It is intended for use in small arms applications and approximates the results from ballistic gelatin tests, in particular.
What follows is a walkthrough for use on Windows desktop calculator, set to scientific View Mode. All units will be in English measurements.
(My apologies to you calculator wizards for the "baby steps.")
A. Variables (what you need to make it work)
1. Bullet diameter (bd) in inches
2. Bullet weight (w) in grains
3. Impact velocity (v) in feet per second.
4. Bullet shape factor (Cd) unitless
(assume a value of .52 to .55 for most spitzer bullets, .55 to .57 for flatnose to roundnose bullets, .70 for mushroomed, and .83 for
flat cylinder.)
''B. Procedure
1. Find ballistic coefficient
a. Divide bullet diameter by 12, press [=] or [enter]
b. Square [x^2] result of (a)
c. Multilply result (b) by pi and divide by 4
d. Multiply (c) by bullet shape factor, press [=] or [enter]
e. Store this result using [M+] key
f. Clear display using [C]
g. Divide bullet weight by 7000, press [=] or [enter]
h. Divide result of [g] by stored value [MR] and press [=] or [enter] to get ballistic coefficient
i. Clear previously stored value using [MC] and store ballistic coefficient using [M+]
(Note: This ballistic coefficient will look entirely different than the one you may be accustomed to seeing in ballistics tables.)
2. Determine average kinetic energy
(There are two ways to do this, both easy.)
a. Divide impact velocity by 2, press [=] or [enter]
b. Square result (a) by [x^2] multiply by bullet weight, press [=] or [enter]
c. Divide result (b) by 7000, divide again by 32.174, divide once more by 2; press [=] or [enter] to obtain average kinetic energy
(Alternate method
a. Square impact velocity with [x^2], multiply by bullet weight, press [=] or [enter]
b. Divide result (a) by 7000, divide again by 32.174, divide once more by 2, divide finally by 4; press [=] or [enter] to find average kinetic energy.
(Explanation: The "average kinetic energy" is important because the bullet stops within the medium. In other words, the velocity
becomes zero.)
3. Obtain unadjusted penetration value
a. Multiply average kinetic energy result from (2c) by stored ballistic coefficient by using [MR]
b. Divide by the constant 52130, press [=] or [enter]
c. Using the result of (b), hit the [x^y] key and enter 0.25; press [=] or [enter]
d. Multiply result of (c) by 12, then hit [=] or [enter] to obtain the unadjusted penetration value (in inches)
e. Clear memory with [MC} and add result (d) back into memory with [M+]
f. Clear display with [C]
4. Obtain estimated penetration (in inches)
a. Estimate bullet surface by dividing bullet diameter by 2 and multiplying by pi; hit [=] or [enter]
b. Use [+/-] key to make result (a) negative
c. Add result of (b) to the memory using the [M+] key; clear display with [C]
d. Review stored value using [MR]
(Note: If this value is zero or a negative number, then stop right here! There is no penetration!)
e. Multiply the value from (d) by 3 for the estimated minimum penetration or by 5 for estimated maximum penetration.
f. Of course, hit [=] or [enter]
I can offer explanations if anyone is interested.
<whew!>
Hit [=] or [enter].
(simplified for desktop calculator)
This is just one portion of the penetration predictor that I worked up some time back from my own independent research (i.e. I ain't read it from no books.) It is intended for use in small arms applications and approximates the results from ballistic gelatin tests, in particular.
What follows is a walkthrough for use on Windows desktop calculator, set to scientific View Mode. All units will be in English measurements.
(My apologies to you calculator wizards for the "baby steps.")
A. Variables (what you need to make it work)
1. Bullet diameter (bd) in inches
2. Bullet weight (w) in grains
3. Impact velocity (v) in feet per second.
4. Bullet shape factor (Cd) unitless
(assume a value of .52 to .55 for most spitzer bullets, .55 to .57 for flatnose to roundnose bullets, .70 for mushroomed, and .83 for
flat cylinder.)
''B. Procedure
1. Find ballistic coefficient
a. Divide bullet diameter by 12, press [=] or [enter]
b. Square [x^2] result of (a)
c. Multilply result (b) by pi and divide by 4
d. Multiply (c) by bullet shape factor, press [=] or [enter]
e. Store this result using [M+] key
f. Clear display using [C]
g. Divide bullet weight by 7000, press [=] or [enter]
h. Divide result of [g] by stored value [MR] and press [=] or [enter] to get ballistic coefficient
i. Clear previously stored value using [MC] and store ballistic coefficient using [M+]
(Note: This ballistic coefficient will look entirely different than the one you may be accustomed to seeing in ballistics tables.)
2. Determine average kinetic energy
(There are two ways to do this, both easy.)
a. Divide impact velocity by 2, press [=] or [enter]
b. Square result (a) by [x^2] multiply by bullet weight, press [=] or [enter]
c. Divide result (b) by 7000, divide again by 32.174, divide once more by 2; press [=] or [enter] to obtain average kinetic energy
(Alternate method
a. Square impact velocity with [x^2], multiply by bullet weight, press [=] or [enter]
b. Divide result (a) by 7000, divide again by 32.174, divide once more by 2, divide finally by 4; press [=] or [enter] to find average kinetic energy.
(Explanation: The "average kinetic energy" is important because the bullet stops within the medium. In other words, the velocity
becomes zero.)
3. Obtain unadjusted penetration value
a. Multiply average kinetic energy result from (2c) by stored ballistic coefficient by using [MR]
b. Divide by the constant 52130, press [=] or [enter]
c. Using the result of (b), hit the [x^y] key and enter 0.25; press [=] or [enter]
d. Multiply result of (c) by 12, then hit [=] or [enter] to obtain the unadjusted penetration value (in inches)
e. Clear memory with [MC} and add result (d) back into memory with [M+]
f. Clear display with [C]
4. Obtain estimated penetration (in inches)
a. Estimate bullet surface by dividing bullet diameter by 2 and multiplying by pi; hit [=] or [enter]
b. Use [+/-] key to make result (a) negative
c. Add result of (b) to the memory using the [M+] key; clear display with [C]
d. Review stored value using [MR]
(Note: If this value is zero or a negative number, then stop right here! There is no penetration!)
e. Multiply the value from (d) by 3 for the estimated minimum penetration or by 5 for estimated maximum penetration.
f. Of course, hit [=] or [enter]
I can offer explanations if anyone is interested.
<whew!>
Hit [=] or [enter].
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