School Project On Recoil


Dear Technoid,

I am a ninth grade student doing a science project on weapons. One topic my teacher wanted me to look into was shotgun recoil. I had hoped to go back a couple of years and see how people were able to reduce the recoil on their shotguns compared to how we reduce the recoil of our shotguns today.

Unfortunately, I have failed and I am really seeking information. I would really appreciate it if you could e-mail me some information on how people are able to reduce the recoil of their shotguns today compared to how they used to do it maybe 2-5 years ago. I will relate shotgun recoil to Newton’s Third Law of Motion which deals with Momentum if I can get the proper information.

Thanks!!

Luke
Minnesota

Dear Luke,

Always happy to help someone in school. So many school teachers are blindly anti-gun that it is nice to know that some are still open minded.

A shotgun (any gun) has two types of recoil. There is the mathematical type a la Newton and there is the “felt” or “subjective” type.

Here’s an example of the difference: The formula for mathematical free recoil which I use has only three real variants-

1) the weight of the gun,
2) the weight of the ejecta (shot, wad and powder) and
3) the speed of the ejecta.

A constant is used for the escape velocity of gas, but that gets complicated and plays only a small part. Gun weight, ejecta weight and ejecta speed are the main things.

Subjective or felt recoil is entirely different. Take a given shotgun and shell, hold it against your shoulder and fire it. You will feel a certain amount of recoil. Now take exactly the same gun and shell, hold it against your nose and fire it. Even though the mathematical recoil hasn’t changed, what you felt sure has. A poorly fitting shotgun stock or poor shooting technique will increase subjective recoil even though Newton’s mathematical recoil remains the same.

Going back 2-5 years to trace efforts to reduce recoil really isn’t far enough. If you go back 15 years, then you can make some real comparisons.

One of the standard ways to reduce mathematical recoil is to increase the weight of the shotgun by adding a “recoil reducer”. This usually takes the form of a tube of lead or mercury placed in the buttstock. Sometimes the lead is on a spring so that stretches out the recoil pulse in addition to just adding good old Newtonian tonnage. The Mercury recoil reducers, in addition to adding weight, also have an orifice which permits the mercury to flow through at a certain rate during recoil, somewhat like the lead and spring. The idea is again to stretch the recoil pulse out. The area under the recoil curve remains the same, but the peak of the curve is lowered and flattened.

Another relatively recent method of reducing recoil is by using a muzzle brake or “porting”. These are simply holes or slots drilled in near the muzzle of the barrel. Their intent is to redirect gas so as to reduce a bit of the “jet effect” of the gas escaping straight forward (thus recoiling straight back) at the muzzle. The method works very nicely on tanks, howitzers, high power pistols and high power rifles, but shotguns don’t generate gas at any where near the same velocity, so it is only marginally effective. The recoil formula which I have takes into account the escape velocity of the gas, but not its vector. Porting changes the vector of a bit of the gas.

Recoil pads and pneumatic stocks can very much reduce subjective recoil, but not mathematical recoil. A pneumatic stock has sort of a shock absorber built into the stock so that it collapses on recoil. They VERY much reduce the subjective felt recoil. Rubber recoil pads work the same way, but much less so. Both of these devices don’t lower mathematical recoil at all. What they do is to streeeeetch it out over a longer period of time- more like a slow push than a sharp poke. If you add the recoil up, the total stays the same, but because it is delivered at a much slower rate, it seems like less. Slower burning shotgun powders are also claimed to do the same thing, but I have never been able to notice the slightest difference with them.

Another effective method of reducing both mathematical and subjective felt recoil is to lower the amount of shot in the shell and/or the velocity of the shell. A few years ago, the standard target load had 1-1/8 oz of shot. Today the 1 oz load is very popular because it has 19% less recoil. Of course fewer pellets give you less chance of hitting the target, but many people feel that the trade-off is worth it.

One final method of reducing subjective felt recoil, though not mathematical recoil, is to switch from fixed breech gun (O/U, SxS or pump) to a semi-auto operated by gas. Like the other examples of pneumatic stocks and recoil pads, the gas gun doesn’t reduce mathematical recoil, but it seems to shoot softer because the cycling of the gas action spreads the recoil pulse out over a longer period of time. Again, the area under the recoil curve stays the same, but the curve has less sharp peaks.

I hope that it enough to get you going on your project. If not, write back.

Best regards,

Bruce Buck
Shotgun Report’s Technoid

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