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Data
| Weight / Length Equivalents | Conversion Factors | Other Equivalents |
| 7000 Grains = 1 Pound | Pounds x 7000 = Grains | 2 PI radians = 360 degrees |
| 437.5 Grains = 1 Ounce | Ounces x 437.5 = Grains | 1 MOA = 1.047" (per 100 yard radius) |
| 15.43 Grains = 1 Gram | Grains x .0229 = Ounces | 1 MOA = 2.908 centimeters (per 100 meter radius) |
| 25.4 Millimeters = 1 Inch | Grams x 15.4324 = Grains | 1 mill = 3.439 MOA |
| 1 mile = 1760 yards | Grains x .0648 = Grams | |
| 1760 yards = 5280 feet | Inches x 25.4 = Millimeters | |
| Millimeters x .03937 = Inches | |
| Loads Per Pounds of Powder (amt.grs = loads) |
| 5 gr. = 1400 | 40 gr. = 175 | 75 gr. = 93 |
| 10 gr. = 700 | 45 gr. = 155 | 80 gr. = 87 |
| 15 gr. = 466 | 50 gr. = 140 | 85 gr. = 82 |
| 20 gr. = 350 | 55 gr. = 127 | 90 gr. = 77 |
| 25 gr. = 280 | 60 gr. = 116 | 95 gr. = 73 |
| 30 gr. = 233 | 65 gr. = 107 | 100 gr. = 70 |
| 35 gr. = 200 | 70 gr. = 100 | |
Standard Deviation:
Example: 5 shot string, velocity's of 1020, 980, 1000, 1015, 985.
First, add the five velocity's and take their average: 1020, 980, 1000, 1015, 985
The five velocity's add up to 5000 fps. Their average is 1,000 fps (5000/5)
Next subtract the average from each velocity and square the difference.
Add up the squared differences (1250) and divide by 4 (the number of velocity's minus one).
Always divide the number of measurements minus one. The result is 312.5 or 17.68: (17.68 x 17.68 = 312.5).
Muzzle Energy:
Weight of bullet (in grains) x velocity (in foot seconds) x velocity x 0.000002218 = energy in foot pounds.
Example: 100 grain bullet at 3000 ft/seconds -> 100 x 3000 x 3000 x 0.000002218 = 1996 foot pounds energy.
Momentum In Pound Seconds:
Multiply the bullet weight in grains by the velocity at impact. Divide the product by 226,000 ( a gravimetric Constant).
Example: 45 caliber 240 grain bullet 200 yard velocity of 985 fps.
240 x 985 = 236400 divided by 226,000 = 1.046 pound-seconds momentum.
Coefficient of Variation:
The coefficient of Variation shows the standard deviation as a percent of the average and is a more reliable measure of a loads consistency.
The smaller the CV the less variation there is "relative to the average".
The smaller the CV the less variation there is "relative to the average".
Divide the average into the standard deviation and multiply the result by 100.
From the above example of standard deviation: The S.D. is 17.68. The average is 1000.
Example:17.68 (SD) divided by 1000 (velocity) = 0.01768 x 100 = 1.768. The CV is 1.768.
Sectional Density:
The formula for SD is: SD + WG /7000 x D2 where WG is weight is in grains and D is is the bullets diameter in inches.
Example: For a 180 grain .30 caliber bullet, SD = 180/7000 x .308 squared.
Divide the bullets weight in grains (180) by the number of grains in a pound (7000), which yields .2571428.
Next square the bullets caliber in inches (.308 x .308) which gives .094864 and divide into .2571428 which yields .2710638.
This rounds off to an SD of .271.
Greenhill Formula:
The formula to determine the correct rate of rifling pitch for bullets of usual construction (lead alloy or jacketed) is known as the "Greenhill Formula".
(1) Determine the length of the bullet in calibers. (Bullets length in inches divided by the bullets nominal caliber).
(2) Divide 150 (a constant) by the bullets length in calibers.
(3) Multiply the result of step two by the bullets "nominal" caliber. This will give the desired rifling twist rate.
Example:To find the correct twist for a .30 caliber 220 grain bullet 1.35 inches long.
1.35/.30 = 4.5 calibers.
150/4.5 = 33.33.
33.33 x .30 = 9.999 or 1 in 10 inch twist.
Radian:
A unit of plane angle, equal to 180/PI (or 360/(2PI)) degrees, or about 57.2958 degrees, or about 57 DEG 17'45"
MOA:
Minute of Angle (or Minute of Arc). is a unit of angular measurement, equal to one sixtieth (1/60) of one degree.
Since one degree is defined as one three hundred sixtieth (1/360) of a circle, 1 minute of arc is 1/21,600 of the amount of arc in a closed circle.
Calculating the physical equivalent group size equal to one minute of arc can be done using the equation: equivalent group size = tan(MOA/60) * distance.
In the example previously given and substituting 3600 inches for 100 yards, 3600 tan(1 MOA/60) inches = 1.047 inches.
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