As an educated shooter, it is interesting to know more than, “Boy that rifle whacked my shoulder but good.” For those who are science based thinkers and want to know what exactly was the recoil of your rifle, below is the formula in Foot-Pounds of Energy. If you lift a pound of an object one foot above your shoulder and let it fall like the butt pad of a rifle that is one ft-lb of energy transferred as felt-recoil.
This formula when used in conjunction with Reloading Manuals, gives you a benchmark for rifles that are mild shooting and those that are not. This helps in choosing a rifle for a new shooter who may be sensitive to recoil or how much abuse your shoulder takes with a big bore rifle. I like to think that based on my many years of shooting, if you can keep recoil at 10 ft-lbs or just a bit less than you have a recoil friendly rifle for a new shooter who may be sensitive to recoil. Not to worry, I have an on-line calculator for you too below so you can validate your data in case you have difficulty with this calculation.
Recoil Calculation Formula
Recoil in Ft- Lb = ((((Wb+(Wp x 1.75)) x Vm)/Wr)/7000)^2 x Wr / 64.4
Where:
Wb = Weight of Bullet in grains
Wp = Weight of powder in grains
Vm = Muzzle Velocity in fps
Wr = Weight of Rifle in pounds
Ga = Acceleration of gravity 64.4 fps/sec
This formula can be placed into a spreadsheet if you like and you can play with the variables of Bullet, Powder, Muzzle Velocity and Weight of your rifle. Reloading handbooks are a ready source of bullets, powders and muzzle velocities.
Here is an example for a 243 Winchester:
Wb=100 grains
Wp=43 grains
Vm=2900 fps
Wr=8 pounds
Take the weight of the powder and multiply by a factor of 1.75 = 75.25. Add this to the weight of the bullet 100 + 75.25 = 175.25. Now multiply this by the muzzle velocity 175.25 X 2900 = 508225. Take the 508225 and divide it by the weight of the rifle in pounds. 508225/8 pounds = 63528.125. Now divide this by 7000 grains per pound. 63528.125/7000 = 9.075. Ok, we are almost there. Now square this result 9.075^2 = 82.355. Multiply this by the weight of the rifle in pounds, 82.355 x 8 = 658.845. Finally divide this by the acceleration of gravity 64.4 fps/sec = 10.23 ft-lbs Recoil. I rounded these numbers a bit in my spreadsheet and got 9.9 ft-lbs recoil, a tenth of a pound difference. Or use this calculator below which does it easily and includes products like recoil velocity and recoil impulse. This is a great way to validate the formula findings. If you round your intermediate data it may vary slightly from the on-line calculator.
http://www.shooterscalculator.com/recoil-calculator.php
Jim Carmichel of Outdoor Life reveals this formula in an article where I wrote down the formula as an equation and validated his findings on the 30-30 Winchester See below.
http://www.outdoorlife.com/articles/guns/rifles/2007/09/calculate-recoil-energy
In an earlier article at New Hampshire Rifleman we discussed the use of recoil pads from both Sims Vibration Laboratories and those from Pachmayr Decelerator pads that can cut the felt recoil in half. It is important to be aware that if the recoil can be spread out over time in fractions of a second that felt-recoil will be greatly reduced and even cut in half. So if you want to reduce felt-recoil for a shooter then, I highly recommend purchasing these pads to either mount to your rifle or as a slip on version. I own these pads for my rifles. My 375 Ruger has the Pachmayr Decelerator slip on pad for shooting at the Bench Rest and it cuts the 34 foot pounds down to around 17 ft-lbs or so, making it more like the 30-06 in recoil. See your local retailer to purchase these pads.
Good Hunting! © 2015