Taming Recoil

How to manage recoil –

Try taming recoil with proper shooting techniques before going to the expense of purchasing and mounting recoil-managing hardware. Once you’ve learned the basics of recoil management you’ll make more informed choices when purchasing the hardware. Plus, the equipment will be far more effective because you used the proper techniques, making you happier with the results!

If you’ve already read this info, skip the palaver and go directly to the RECOIL CALCULATOR. (development copy at http://laspositasgroup.com/Recl1Frm.php)

Common Questions:

Why does it hurt so much when I shoot my shotgun? After all, it’s only a 20 gauge? It’s a lot less powerful than the 12 gauge and it doesn’t weigh nearly as much.

Why does my 30-30 lever gun hurt so much when I shoot it? It’s not nearly as powerful as the.308 Winchester or 30-06, let alone the .300 Winchester Magnum.

(answers at end of article!)

A Brief History of recoil:

From sometime during or before the 10th century AD, when an ancient Chinese touched a match to a tube with filled with a pyrotechnic powder, recoil has been an amazing and mysterious phenomenon. Rocks, darts, and other “interesting” items were likely added later. These additions added to the kick-back of these primitive firearms. Recoil as a phenomenon has continued to be a key factor in firearm, cannon, and fighting vehicle design throughout the ages since.

To be sure, the ancient fire lance was pretty heavy and the powder was really weak by modern standards. Even so, we can be reasonably sure that the nascent gunsmiths in ancient China had to account for recoil in designing the tube and its mounting on the long stick and blade that made up the rest of the lance. Most of us, however, don’t have to worry about lances, shaking wings off of aircraft or breaking the keels of ships. But, we do worry about that bruise on the shoulder, or the ring-shaped scar we might get when pulling the trigger on our favorite high-powered rifle or shotgun. Indeed, a few thousand folks visit emergency rooms with recoil-induced injuries every year.

While the fire-lance would be closer to the effect of a medium-sized hobby rocket today, the effects and underlying physics are identical to the physics of firearm recoil. In this, we have a projectile and propellant package inside a tube. Igniting the propellant expels the combustion gases along with the projectile(s). The propellant gases will accelerate even more after the projectile leaves the bore, adding to the impulse that causes the firearm to move into the shooter.

Newton tells us that the impulse generated by accelerating the bullet and powder gas is simply the sum of the mass times the velocity of the stuff being launched. The impulse in turn generates the same level of momentum in the gun but in the opposite direction of the powder and projectile (remember “equal and opposite?”). Further, the gun doesn’t instantaneously jump from motionless to its free-recoil velocity. The projectile and powder take a little bit of time to travel down the bore. This is the minimum time for accelerating the gun too.*

Here are a few terms to consider when we talk about recoil:

Free Recoil — A description of the rifle velocity, momentum, and energy when not supported. (Visualize the rifle suspended horizontally with a string and free to swing.)
Felt Recoil – The impression the shooter gets from kick. Felt recoil Is only loosely connected to free-recoil energy and momentum (impulse). Firearm design can strongly influence felt recoil. Proper shooting technique and appropriate accessories can also lessen the intensity of felt recoil.
Weatherby Eye — That ring-shaped scar one gets from a rifle scope eyepiece cutting around the eye-socket during recoil. (This could be an example of felt recoil gone awry!)
Muzzle brake – A device mounted on the end of the barrel that deflects part of powder gas to the side or slightly backward. Muzzle brakes work — even better when the powder/bullet weight ratio is high.
Recoil Pad – A resilient pad mounted on the butt stock to reduce the sharpness of felt recoil.
Monte Carlo Stock – A stock with in improved alignment of barrel and buttstock to help minimize muzzle rise. The alignment and the prominent cheekpad are designed so that the stock move away from the face during recoil.

How do we prevent bad things from happening when we get kicked by the rifle or shotgun?

Consider what happens with the body when the rifle pushes back on your shoulder. Whether you have tensed up or not, your shoulder and upper body will move back while the muscles and tendons take up slack. In the meantime your head is standing still and won’t move with your shoulder until that slack is taken up. What does this mean? From your eye’s perspective the rifle and the rigidly mounted scope jumps back, significantly closing the gap afforded by eye-relief.

Noel S., a prominent member of our local gun club, passed along this bit of advice given him by his father about fifty years ago. Paraphrasing, the advice** is the keep one’s chin forward with the head as far forward on the rifle as the butt on the shoulder will allow. This takes up a lot of the slack in the various joints alluded in the previous paragraph, reducing the chances of the scope banging one’s eye socket. Even if this isn’t enough to completely prevent contact, the speed of impact will be reduced by having the body more nearly one with the rifle to start with. Coincidentally, this head position also helps reduce any tendency to bruise the shoulder because the rifle doesn’t have space to accelerate before striking the shoulder.

Make sure there is tight contact between the shoulder and the recoil pad. Making sure one’s body is tightly welded to gun reduces felt recoil regardless of whether sling is used. Less than a quarter-inch space between the butt and the shoulder is enough for the full recoil velocity to be developed! (Leads to bruises and worse!) The shoulder, lower, neck, and upper body add to the mass being accelerated. The larger mass reduces velocities and the kinetic energy available to do damage. You can go here to see what the distance is for a an example load: http://laspositasgroup.com/Recl1Frm.php. You can modify the parameters for your favorite load!
Get the butt placed correctly on the shoulder (May seem redundant, but you sure don’t want a heavy kicker resting on your collarbone!)
A sling, preferably in a formal high-power rifle configuration, or in the “hasty sling” mode, will help both make that contact and bring the mass of the supporting forearm into the effective weight of the rifle. This helps minimize the felt recoil by reducing the recoil velocity and energy.
When using a scope, position your head forward with chin leading. Adjust the scope in its mounts so you can use the maximum eye-relief available with the head-forward position.
Heavy clothing helps. We probably won’t be wearing heavy clothing on hot and humid days, so consider wearing a padded vest or a strap-on pad.

The tips above are things you can do without spending a lot of money! Chances are that you’ll want to do more. The manufacturers of muzzle brakes, recoil pads, and more complicated recoil mitigating hardware will be more than happy to help you learn more about their products and how they can help!

ROLE of POWDER GAS

Just how important is the gas in generating recoil? A lot will depend on the ratio of the weight of the powder to the weight of the bullet. We won’t notice the gas contribution when the ratio is less than about 0.15 but it will be clearly noticeable when the powder weighs more than half of the bullet weight. I recently had an interesting email conversation with Tony Williams (http://www.quarry.nildram.co.uk/) where the gas can be a surprising contributor to recoil.

He sent me commentary based on his review of Proceedings of the Ordnance Board held in the Leeds Armouries library reporting recoil tests of the .303 British in the Mark 4 rifle and the Mark 5 (AKA Jungle Carbine) using the Mark VII cartridge. The .303 British Mark VII round uses a 174 grain bullet and about 44 grains of propellant, making the mass ratio about 0.25 and the calculations would suggest that the gas contributes about 60% of the recoil energy (28% of the velocity). The note he sent follows:

“The short-barreled Lee Enfield No.5 jungle carbine has long had a reputation for kicking much harder than the standard No.4 rifle (never having fired one, I can’t verify that for myself!). In part that will be due to its reduced weight, but I have often wondered what the conical flash eliminator contributed to that, since it has a similar shape to rocket Venturi and should in theory add to the rearwards thrust of the escaping gas.

Well, now I know, thanks to a document I found in the Leeds Armouries library on a recent rummage. Official recoil tests** were carried out on the No.4, the No.5 without flash eliminator and the No.5 with flash eliminator. The results were as follows:

No.4 rifle: average recoil energy = 10.06 ft lbs

No.5 carbine without flash eliminator = 12.68 ft lbs

No.5 carbine with flash eliminator = 14.12 ft lbs

So, the reduced weight and shorter barrel added 26% to the recoil, and the flash eliminator a further 11.4%, giving an overall increase in recoil of 40%. A bit noticeable…”

Tony’s anecdote tells us that the gas indeed plays a prominent role in generating recoil. It also suggests the potential reduction in recoil one might see when using properly designed muzzle brakes.

What’s different about this recoil calculator?

Most recoil calculators use a simple multiplier of 1.25, 1.5, or 1.75 times the bullet velocity to estimate the average gas velocity. Some employ a fixed gas velocity of 4000 ft/sec or some other value. This works well enough for most cartridge and gun combinations, but there are times when this technique significantly underestimates the powder gas contribution to recoil. Very large case volumes filled to the gills with powder behind light weight bullets are where this becomes most evident. One example is the the .30-378 Weatherby where one can find loads where there’s more powder than bullet! Low expansion ratio sand LOTS of powder mean that the gun will kick a tad harder than a “standard” recoil calculator would indicate.

The “secret sauce” in the calculator? The ShootersNotes^TM recoil calculator does not use the canonical velocity multiplir or fixed powder gas velocity. More advanced internal ballistics codes like QuickLoad^TM employ a stepwise calculation of bullet, powder burn, and pressures that would be difficult for a high-volume on-line application. Instead ShootersNotes uses an extension of the adiabatic expansion used in the Powley calculator, coupled with a modification of a modification of a very mature tool explosives design tool, to estimate the average gas velocity. Resulting momentum statements are remarkably close to what one would get with QuickLoad!

Got to the recoil calculator now: http://laspositasgroup.com/Recl1Frm.php

Answers to the questions:

Why does it hurt so much when I shoot my shotgun? After all, it’s only a 20 gauge? It’s a lot less powerful than the 12 gauge and it doesn’t weigh nearly as much.

The twenty gauge typically has both a smaller shot weight and powder charge. One of the problems, however, is that the caliber is frequently purchased for small-statured folks like youth and women. The thinking is that a lighter gun is easier to carry. Problem is that lighter weight can result in more recoil energy than the 12 gauge even though the driving impulse is lower!

Why does my 30-30 lever gun hurt so much when I shoot it? It’s not nearly as powerful as the.308 Winchester or 30-06, let alone the .300 Winchester Magnum.

Like the twenty gauge, the “thutty-thutty'” lever action was design as an easily-carried lightweight fire-arm. While a lighter gun is easier to carry, bit that lighter weight can result in more recoil energy than some more powerful cartridge in heavier rifles even though the driving impulse is lower!

Add to this that too many people start with the 30-30, thinking the low-powered rifle is easier to learn with. Not true – it is better to go with a rifle of appropriate weight in the future caliber of choice and use commercial “managed recoil” ammunition for learning and practice or use reduced load handloads for the same purpose. The .308 Winchester, 30-06, .270 Winchester, etc. will likely be heavier than the 30-30 and be designed to better manage recoil than most rifles in 30-30.

The reduced recoil varieties of ammunution are adequate for a lot of big game hunting even though the useable range might be a hundred or so yards less than the full power option., After learning to shoot with good habits in the reduced recoil mode, transitioning to nominal full-power ammunition is straightforward.

* The brief time required for powder gases to clear the bore adds impulse and time to the acceleration profile. Movement of components inside the firearm change the character of the recoil, and can also increase of the time of acceleration seen by the shoulder, but not change the momentum seen by the firearm-shooter system.

** I could have used the advice when I was trying to develop an accuracy load with my .378 Weatherby Magnum in the late 1960’s. Got a welt or two over the eyebrow, but fortunately no broken skin.

Shooters Notes (Development Copy)

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