In deciding what gun to choose, especially for relatively new and young shooters, recoil is a factor. One way of comparing the recoil level of various calibers/gauges, loads, and guns, is by calculating the amount of recoil generated. This is only a limited evaluation of how the gun will actually behave in the shooter's hands. It does not consider burning rates of powder, possible effects of overbore (size of cartridge case relative to bore diameter), oversized bores in some target shotguns, fit of stock to shooter, geometry of gun relative to shooter, and other factors. Nevertheless, comparative recoil calculations are still a useful tool in choosing guns.<br><br>The calculations can be found in Hatcher's Notebook by Major General Julian S. Hatcher, 3rd Ed, 1966, Stackpole Books. Chapters 11-12, pp.253-300 discuss recoil. Especially see pp. 290-291 for a discussion of relevant formulae.<br><br>I have found very helpful the following simplified formula:<br><br> <br>R = { [ ( b V + 4600 P ) divided by 7000 ] quantity squared } all divided by 64.3 G<br><br><br>R = Recoil Energy expressed in foot pounds.<br><br>b = bullet weight in grains.<br><br>V = Velocity of bullet.<br><br>P = Powder weight in grains.<br><br>G = Gun weight in pounds.<br><br>For example, let's compute the recoil of a .30-06 rifle weighing a total of 8 lbs. (including scope, ammo, sling, etc.) shooting a 150 grain bullet at 2900 feet per second. A typical gunpowder may weigh 50 grains. Thus we know the following:<br><br>b = 150<br><br>V = 2900<br><br>P = 50<br><br>G = 8<br><br>Therefore,<br> <br>R = { [ ( 150 X 2900 ) + ( 4600 X 50 ) divided by 7000 ] <br><br> quantity squared } all divided by ( 64.3 X 8 ) .<br><br>Ergo, R = 17.5 foot pounds.<br><br>Note 64.3 = 2 X gravity<br><br>4600 = a physical constant<br><br>I apologize for the use of words rather than the conventional mathematical symbols, but that's a little outside of my usual area of work. I hope that the rarely seen the formula is as useful for others as it has been for me.<br><br>John<br>

John,<br><br>Good info. This will probably provide a fairly good estimate, and if used for comparison will at least have the same errors for both weapons. The two confounding factors I see being that different types of powders are going to give different results (although they may just be accounting for the weight mostly), and one needs a meter to measure bullet velocity (although most reloading manuals give an approximate velocity). If using factory loads, you might know the velocity but not the weight of the powder. <br><br>As an aside, the 7000 is likely a conversion from grains to pounds, in case you are interested.<br><br>Greg

Big numbers always give me a headache. I do know that I first shot a .30-06 (03 Springfield) when I was five years old. I used a kneeling position, my dad supported the weight of the weapon on his hands, held palm up, so that they did nothing to help control the recoil. Kicked like a mule, but I kept shooting it. Did a 12 ga Model 12 same day, very different kick...<br><br>Your info is very interesting, thanks...

Greg,<br><br>I think you're right about the 7000. <br><br>What I do for factory loads & handloads is just to assume the quoted or predicted velocity is accurate. If I have a significantly different barrel length from the norm for that cartridge, I try to allow for that. For factory loads, I also check the data for several similar handloads, and make composite estimates of the amount of gunpowder used. I know, those are kind of crude fudge factors but they seem to yield answers that jibe more or less with observed reality. You're right though; a chronograph would make it a lot more precise.<br><br>OBG,<br><br>I know what you mean. If you run the numbers, the .30-06 & 12 ga. seem to have about the same recoil force in terms of foot pounds of energy, but they really do feel a lot different.<br>And the recoil from black powder loads gives a very different feel from otherwise similar smokeless powder loads. It's more like a gradual push than a kick. Shooting a load in a gas operated automatic will also moderate the felt recoil in comparison to a gun that is not gas operated.<br><br>I find the formula most useful for helping to evaluate something I can't shoot for myself. For instance, I can't really judge the recoil in my son's short-stocked shotgun. I've got my arms wrapped all around it. And I frequently bang my nose with my thumb when the gun recoils. My own shotguns are different enough that shooting the same loads will feel differently in my gun than in his gun. That's where the formula helps to predict how it will feel to him, at least in comparison to other known satisfactory loads & guns. <br><br>I'm glad you guys like it.<br><br>John