Expressed in foot/pounds of energy or momentum:
This is also called "free recoil."
The formula is as follows:
Velocity (in fps) squared, divided by 7000, divided by 64.32 times the bullet weight (in grains).
The velocity leaving the muzzle is the one we are interested in. The lower velocity out at the distant target is not involved in recoil measurements
Expressed in a term called "Recoil Energy":
There is a popular formula for comparing recoil between various rifles and the ammunition being fired. The formula reads as follows:
RE= 1 over 2GW times bwbv+ cwC over 7000 and this second half of the equation is squared.
The letters translate as follows:
RE= recoil energy
G= gravity constant of 32.2 fps per second
W= gun weight in pounds
bw= weight of bullet in grains
bv= muzzle velocity in fps
cw= Weight of powder in grains
C= 4700 math constant (gas velocity)
(This formula comes from the Stackpole book, "The Firearms Dictionary.")
Expressed as "perceived or felt" recoil which is commonly called "kick":
With a pistol hand held - the barrel is generally above the wrist and upon firing, the wrist pivots and the entire arm is moved upwards at the elbow, allowing the recoil to twist the pistol upwards which reduces the recoil felt by the hand, arm and body.
With a rifle or shotgun barrel - held against the shoulder, recoil is directed almost straight back in a manner causing the shoulder to absorb the majority of that reactive force. The shooters cheek will also absorb some recoil if he is pressing into the cheek piece firmly.
The gun does recoil upwards due to bending of the body spine and hips but the recoil has mainly been straight back into the shoulder.
Speaking now of shoulder mounted arms, if the gun is not held tightly against the shoulder, the recoil is felt more sharply and strongly because the gun is kicked back against the shoulder until its movement is stopped by the painful compression of body tissue. Thus a loosely held rifle increases the "felt" recoil.
When the gun is properly held tightly against the shoulder the body tissue is pre-compressed and some portion of the weight of the body mass is added to the weight of the gun.
Mathematically the recoil force is the same in both cases but the shooter feels much less recoil when the gun is pressed firmly against the shoulder.
The 45-120 has a larger powder case capacity and like ALL black powder cartridges it must be "filled" with black powder for both safety and accuracy.
Using say a 500 grain lead bullet, muzzle velocity speeds in the range of 1400 fps to 1800 fps can be obtained.
By comparison, the 45-70 case using the same bullet would produce 1150-1250 fps.
If both these rifles weighed the same, the 45-120 would produce approx. 35% stronger felt recoil than the 45-70.
The Sharps rifles generally weigh 11.0 pounds to 13.5 pounds and average about 12.2 pounds. Buffalo hunters who commonly expected to fire more than 100 shots at one herd, purchased special heavy barrel rifles weighing 14 to 18 pounds. Such heavy guns were fired off crossed sticks, a rolled blanket or other suitable support and not expected to be fired from a standing position.
The felt recoil from such a heavy gun would of course be very small and enabled even a small sized person to fire large strings of shots without excessive soreness in their shoulder. The massive barrel weight also heated up very slowly, allowing the hunter to fire many more shots before having to cool down the barrel.
When shooting from a standing, kneeling or sitting position, the body is free to move with the recoil of the gun but in the prone position or when shooting from a bench, the body does not freely move and therefore absorbs much more of the recoil, giving the effect of a harder kick to the shooter.
For the above reasons, it is somewhat useless to quote foot/pounds of recoil and the shooter should instead consider their own body weight, gun weight, ammunition type, shooting position, duration and amount of shots to be fired in one session...etc.
It should be specially noted, when the same bullet weight is fired using both a smokeless powder and a black powder charge to obtain the "same" muzzle velocity, the felt recoil will be somewhat greater from the black powder charge because the weight of the black powder charge is much heavier than the smokeless powder charge and this weight of powder has to be factored into the total weight of what you are pushing out the muzzle.
However, since smokeless powder will keep accelerating the bullet for most of the barrel length while black powder ceases to impart much significant acceleration after about 8-10 inches of bullet travel, the overall felt recoil of black powder is usually smoother and less of a jolt than is felt with smokeless charges giving the same muzzle velocity.
The use of a properly made shoulder pad reduces felt recoil by spreading the force across a larger area of the shoulder as well as having some absorptive property which absorbs the pressure force and releases it more slowly than it received it.
When properly fitted, this usually allows all shooters to fire a long string of shots from a heavy caliber rifle without the shoulder being abused or bruised.
Use of a "recoil pad" on the butt stock is not nearly enough protection compared to the use of a good shoulder pad.
Finally, I offer some words of encouragement to shooters who may have had an unpleasant experience while testing someone’s rifle. If you become a fairly regular shooter and can practice most weeks when weather permits, you will find that your mind and body both adapt nicely to the recoil of the rifle. After a number of weeks or months your shoulder region and muscles toughen up and you will no longer have as much discomfort and in fact most new shooters report that they eventually lose all the discomfort caused by recoil along with any tendency to flinch or yank the trigger.
For Davide Pedersoli & Co.
Dick Trenk
Competition Events Coordinator
Copyright : R.T. Trenk 2003. May not be reprinted without permission of the author.