This was in several years back copy of American Rifleman. I copied it verbatum as it has good things to print and file away for future reference. Sarge
Bullet energy: E = (BW x V 2) divided by 450,400
Bullet energy is probably one of the most useful formulas for hunters. Adequate energy is one of the factors that assure quick clean kills on game. The only numbers necessary are the bullet weight in grains (BW) and the velocity in feet per second (V) Square the velocity then multiply the result by the bullet weight. Divide the entire product by the constant 450,400 and you have the bullet energy in foot-pounds at the velocity chosen. Remember if you want to know the bullet energy at a certain range then you must know how fast your bullet is going at that range
Sectional Density: SD = BW divided by BD 2
Sectional density is a useful number. The higher the SD number the deeper the bullet tends to penetrate; and also the higher the SD the less velocity the bullet loses during it's flight. As a numerical, the SD is the weight of the bullet in proportion to it's cross sectional area. Bullets being of varying diameters on it's length, the cross section area varies too, so for simplicity we divide the bullet weight in pounds (BW) by the diameter in inches squared (BD) There is 7,000 grains in a pound, so to convert to pounds, multiply the bullet weight in grains by .00014 or if it is easier for you, divide it by 7000.
Power Factor: PF = BW x MV
Many action handgun competitions require a minimum "power factor" (PF) or "lower floor" You should check with the specific sport in which you participate for the power minimum and the specific formula, but IDPA, IPSC and NRA Action pistol use a formula whereby you multiply the bullet weight in grains (BW) by the muzzle velocity in f.p.s. (MV) as measured on a chronograph at the shooting event.
I hope these formula's will help you. Print them out and have them tacked on the bullet board for handy reference.
|From: Sarge ||Sent: 2/24/2004 1:44 AM|
Gunrockets, if you do a lot of reloading then you may need this formula too.
Loading Density: LD = I divided by W
With 'I' being the charge weight and 'W' being water.
With any powder, higher loading density means higher pressure but it also can produce greater consistancy. and usually better accuracy. That is why a full case of slow burning powder will usually out shoot a half full case of fast burning powder.
To get the loading density you need to know the case capacity accounting for the space left after a bullet is seated. Here is an easy way to do that. Take a bullet that you will be using and cut a groove on one side of it. It should be running from the heel up to the ogive. Next weigh the case and the prepared bullet together to get the tare weight. (be sure to put a fired primer in the case) Then size the case and fill it full of water. Then seat the prepared bullet to the proper depth. The water it displaces will escape out the groove. Dry off the outside of the water filled cartridge with it's bullet seated and weigh it. The difference between the empty dry case with bullet seated and the water filled one will be capacity of the powder chamber in grains of water. You now know how many grains of powder you can put in the case. But remember you must go by the loading manual. You can not just dump the water weight of powder in and shoot it. But you can pick the powder that will come the closest to the powder weight capacity for the maximum safe and most dense load and there fore the fastest and likely the most accurate load for that cartridge.
So if you were able to get 85 grs of a powder in the case and the water weight happened to be 85 grs then your loading density would be 1 to 1 which would be excellent. If you could only get 40 grs of powder in your case with a water weight of 85 grs then your LD would be .47 loading density, not too good, go to a slower burning powder to up the LD to about .80 if possible. Do you see how it works?