Grains; there is 7000 of them to a pound. It is the measurement used in the shooting sports for bullet weight and powder charges. And it was originally based in England as the weight of a single seed of barley. For those who are metrically inclined the gram = 15.43 grains.
Shotgun Shells Dram Equivalent
Ever notice that shotguns shells use a dram equivalent on the boxes of shells. This refers to the powder charge of modern shotgun shells compared to the equivalent weight in black powder. One dram = 27.34375 grains. A box labeled 3 drams equivalent the velocity will be the same as 3 drams, or about 82 grains of black powder. With 256 drams to the pound, and 16 drams to the ounce and those 7000 grains to the pound we have our units of weight for our shooting sports related conversations. By the way, one dram = 1.77 grams. Another thing to remember when loading your ‘smoke pole’, errr muzzle loader that they usually used volume measurement not weight, to load a black powder charge.
Bullet Kinetic Energy
Remember that we are talking about weight not mass. Weight is mass in a gravitational field, in our case the earth. To convert to mass to satisfy physics computations like kinetic energy we have to convert our grains to mass. The formula is grains/(7000*32.17) or grains/225,190 so the formula for kinetic energy becomes ½ * (grains * velocity^2)/225,200 or more useful KE = (grains * velocity^2)/450,400.
Momentum of Gun & Bullet After Firing
The gravitational field at earth’s surface averages a field acceleration of about 32.17 feet per second per second or ft/s^2. Nothing is really necessarily moving or falling, it’s a physics thing. Everything is rounded to 225,200 to make the paper math easier. But in our society with the ubiquitous electronic calculator many of us have on our phones the more precise 225,190 and 450,380 can be used. Momentum (p) p = grains x velocity/225,200. Momentum has a lot to do with penetration.
Velocity Equals Feet Per Second
It is interesting that we use feet per second for velocity when range is in yards. As a note be aware that nearly all our imperial or English units, we use today were based on their Roman equivalent. The Roman libre or pound is where we get the initials “lb.” for pound. Anyway, our friends across the pond in Europe use meters for both velocity and range. They have grams and meters over there while we deal with grains, feet and yards. The Romans where also to blame for dividing the foot into 12 inches, while originally, they used 16 digits. The Romans used 12 unciae, from which or English ancestors derived both the ounce and the inch, what a process.
Minute of Angle (MOA) & Milliradian (Mil)
Angles we have discussed in the past. The most important for shooters are the minute-of-angle (MOA) and the milliradian (mil). As discussed, the one MOA at one hundred yards is about one inch (1.047) and doubles with a double in yardage. Two inches at 200-yard, 3 inches at 300-yards up to 10 inches at a 1000-yards. About the limit for most of us in shooting sports and way beyond typical hunting ranges. This means that if you shoot a 1-inch group at 100 yards your gun is precise to 1 MOA. MOA is a precision and accuracy measurement. But mils are used to determine range with a mildot scope. Details vary, but you can pretty much dial in the range with a mildot scope.
And that’s about it for today’s review of shooter’s units of measurement.