Recoil’s Time Line

Hi Bruce.

Thanks for the reply. I always enjoy your shotgunnings (writings…) be it on OLN, in the Clay Pigeon, or on the Shotgun

Do you know, other than by the numbers, how one could test (or has tested) the different loads to measure recoil? I understand that pushing 1 1/8 oz of shot to a certain velocity will take a certain amount of energy. But, using the Winchesters as an example, there are some that are more brutal than others. Is there a formal method to test or evaluate the amount of recoil, and duration or type of delivery of that recoil, push versus kick kind of thing? Further what is the relationship if any between chamber pressures (PSI or LUP) and recoil?

We all hear claims that this shell or that shell doesn’t recoil or in the case of the SuperSport AA’s, these kick like a beast! We are generally all covered by the laws of thermodynamics and physics but what is the relationship with slow powders and fast powders in terms of perceived recoil.

In your number crunching, is there a differential calculus equation that could be used to predict type of recoil to complement the amount of recoil. Differential calculus is used to describe and characterize a rate of change. So if powder x will combust in y microseconds and produce z volume of gas, how does this produce and deliver recoil? Also, could an integral calculus equation to measure the area under a curve (measured recoil) be used to characterize recoil? Producing a type a recoil, type b recoil, type c recoil…. That way instead of 3 drams at 1300fps, we may see type b at 1300fps.

Given the different types of guns (gas versus O/U) the contour and length of the curve should change based upon bleed off gas to operate the action. Throw in porting, forcing cones, primer type, hull type, etc. It could be really messy.

What do you think?

Thanks again and take care.


Dear Jim,

I’m not sure that I can help you on this one. There are two kinds of recoil: “Free recoil” as measured by the standard SAAMI recoil formula involving the variables of gun weight, ejecta and speed, and “Subjective recoil”. Subjective recoil is very difficult to measure.

To better understand the term “subjective” recoil, take a standard gun and load and fire it in the normal way from your shoulder. Now take the same gun and shell and fire it, but this time hold the butt against the tip of your nose, not your shoulder. What you just experienced was the same mathematical free recoil, but very different subjective recoil. I don’t know how you quantify that.

When someone tells me his gun “kicks” too much, I always try to get him to describe just how it kicks. Does the pain from the kick radiate through the shoulder, up the back of the neck and into the head? That sounds like pure old free recoil. Does the pain come from a bruised cheek or collar bone? That sounds like felt or subjective recoil as the product of improper gun fit or improper shooting style.

As in most things, it’s all in definition of terms. Of course, if we all defined our terms before we started talking, those endless clubhouse bull sessions would be a lot shorter.

I think that the one area where the SAAMI Free recoil formula falls down is that it doesn’t have a time component. You allude to this and I think that you are spot on. A fixed breech gun and a gas gun of the same weight and using the same shell, have the same mathematic free recoil according to the SAAMI formula. But the curves aren’t the same shape. The areas under the curves are the same, but the time line, or width, of the curves differ. Most people feel that the longer duration recoil pulse of the gas gun has a softer subjective recoil. Obviously, the same thing occurs with slow and fast burning powders, but to a much lesser extent so that it is more difficult for some people to sense.

I don’t think that it would be such a big deal to measure this with some sort of mechanical cradle, slide mechanism, timer to hold the gun. Then just develop a ration of the free recoil/ time in milliseconds or whatever. But- this involves actual shooting and testing. The advantage of the SAAMI formula, and the reason everyone uses it, is that it is pure mathematics and involves no hands on testing. Less work for mother! If there is a lazy man’s way of calculating the time of a recoil pulse, I sure don’t know it- and I know most of the lazy man’s tricks. Trust me on that.

Because concrete measuring of subjective recoil is so difficult, there is little fact to guide the buyer of knickknacks, gizmos and snake oil. The ad-hype guys are quick to spot this and begin to make all sorts of claims. They know they don’t have to prove them, so “white” becomes “WHITER!” and “clean” becomes “CLEANER” just like in the soap suds derby. And of course, “unique” becomes “more unique” for the functionally illiterate. Ain’t democracy great!

At the bottom line, I think that a time-line on recoil is like shotstring. Everyone knows it exists, but most civilians don’t have the equipment to measure it. The after-market guys and factories know this and their ad departments rely on it. The shooters simply throws his money at the problem until he runs out of cash, gives up or finds an answer that pleases him. Each generation of shooters (about every ten years there is a significant turnover in clay sports) seems to have to relearn it all over again. Those who ignore history are doomed to repeat it.

And I’m doomed to repeat this cup of coffee…

Best regards,

Bruce Buck
The Technoid writing for Shotgun Report, LLC
(Often in error. Never in doubt.)

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