I never have been able to use with facility the "gun magazine calculators", probably because they dont name things right, and mash everything into one enormous equation. Its easier to return to your 10th grade high school physics ( or if you are an engineer, what you did at the office yesterday morning ).
Remember that determining free recoil is a two part calculation.
First - you must calculate the velocity of the gun when it recoils and hits your shoulder.
Use the Momentum equation - which merely states mathematically "for every action there is an opposite and equal reaction".
M1V1 = M2V2
M1 is Mass of the ejecta , including shot, wads and powder ( this is one reason Black Powder loads kick so much they really DO have 3 drams of powder -82 grains - rather than 18 grains of Red Dot or somesuch, and all of that has to be included in the "mass of ejecta", but I digress).
V1 is velocity of the ejecta ( muzzle velocity)
M2 is mass of the gun
V2 is velocity of the gun in recoil after firing.
Remember to get Mass from Weight, you must divide by accelleration due to gravity, or "g", which is 32.2 feet per second per second in the English system.
Find M1.
M1 is the mass of the combined ejecta.
Shot weight is 1-1/8 oz. That is 1.125 oz, or 0.0703 pounds.
Divide by 32.2 , and the result is 0.00218 slug.
Wad - Hornady Versalite - weighs 37 grains. Divide by 7000 to convert to pounds = 0.0053. Divide by 32.2 = 0.00016 slug.
Powder - 25 grains Unique. Divide by 7000 to convert to pounds = 0.0036 pounds. Divide by 32.2 = 0.00011 slug
Sum all the numbers
Therefore M1 is (0.00218 + 0.00016 + 0.00011)= 0.00245
Find M2.
Assume gun is 7.5 pounds. Divide by 32.2 and the result is 0.2329. Therefore M2 is 0.2329.
So....
M1V1 = M2V2 ( 0.00245 ) ( 1350 fps) = (0.2329) V2
Rearrange and solve for V2
M1V1 / M2 = V2 or ( 0.00245) (1350) / (0.2329) = 14.20
V2 = 14.20 feet per second in recoil.
Substitute V2 into the Kinetic Energy Equation, Ke = 1/2 MV^2 where V^2 indicates "Vee Squared".
Where M is M2 from above.
Therefore:
Ke = 1/2 (0.2329) ( 14.20^2)= 23.48 foot pounds of Recoil, for a 1-1/8 oz load at 1350 fps in a 7.5 pound gun.
Using the same methodology , given a 1-1/4 oz. shot load, a Hornady Versalite wad, 19.5 grains of GD, for an M1 of 0.00268, and a V1 of 1100 fps,
We arrive at a recoil velocity, V2, of 12.66 fps.
Plugging this into the Kinetic Energy Equation, Ke=1/2MV^2,
we get Ke = 18.66 foot pounds.
CONCLUSION
The 1-1/8 oz load at 1350 fps has 23.48 foot pounds of recoil.
The 1-1/4 oz load at 1100 fps has 18.66 foot pounds of recoil.
The heavy shot charge loading kicks less, and will be a more pleasant companion for a day afield. Burrard discusses this a bit in The Modern Shotgun.
Whether or not the gun "kicks" you badly, includes psychological and physiological factors not subject to easy calculation.
Hope this helps a bit.
Regards
GKT
Last edited by Greg Tag; 12/17/06 06:24 PM.
