Calculating recoil

[robinghewitt]

Recoil is very easy to calculate if you have the muzzle velocity but it means very little.

But as recoil is very much like holding the gun above your shoulder and then dropping it. I thought it might be fun to calculate how high above my shoulder I would have to drop the gun from to feel the same pain as firing it ::

That gives a very "real world" meaning to recoil. If I would rather not drop the gun from that height on to my shoulder then I probably don't want to fire it.

Here's a worked example, a 10 bore at 1000 ft/s from an 10.5 pound Bess. How painful is that?

First you calculate the velocity of the gun.

The ball weighs 0.1 lbs the gun weighs 10.5 lbs, 1000 ft/s

1000 x 0.1 / 10.5 = 9.52 ft/s

After firing the gun is moving backwards at 9.52 ft/s, from how high would I have to drop it to achieve 9.52 ft/s?

Simple, square it and divide by 64

9.52 x 9.52 / 64 = 1.416 feet = 17 inches

Would I willingly drop that gun 17 inches on to my shoulder? :hmm: :results: :crackup:

 

[roundball]

9.52 x 9.52 / 64 = 1.416 feet = 17 inches
Would I willingly drop that gun 17 inches on to my shoulder?

:hmm: :hmm:
...is it possible there might not quite be a direct association with that test, and with the actual "push" of recoil from a pre-mounted (shouldered) rifle
::

 

[weirdjack]

Recoil on your shoulder is not quite that cut and dried though. A lot of factors to consider...stock shape, buttplate, weight, etc...all affect what recoil gets to you. And on heavier guns (your heavy Bess), their own weight will absorb some the "opposite reaction" first. Plus...granulation of powder comes into play also. If you take a given bore, ball, and velocity combination....then shoot it using different granulations of powder (3f, 2f, and 1f), the perceived recoil will probably be quite different in each case. Due to their barious burning rates.
There were some tests done in I think it was August issue of Muzzleblasts which looked into this subject and show it in a nice spreadsheet form. An interesting read.
Jack

 

[robinghewitt]

What happens when you pull the trigger is hard to appreciate without the benefit of ultra slow motion cinematography, but it is very predictable :thumbsup:

The gun moves back as the ball moves forwards. Assuming this Bess has a 42 inch barrel, the gun will move 0.4" so I suppose you do have a little bit of warning before it hits you :hmm:

OTOH as it moves the 0.4" in the time it takes the ball to move up the barrel it may not help much. I don't think the shooter really figures much in the equasion until after the ball is on it's way. People are soft squidgy things when compared to iron and walnut ::

 

[weirdjack]

Hey, don't take my word
Read the Muzzleblasts article. It has the methodology used and the results of some very interesting testing on this exact subject.
Jack

 

[robinghewitt]

:hmm: We don't get Muzzleblasts over here, we get Black Powder Newsletter :thumbsup:

 

[weirdjack]

:hmm: We don't get Muzzleblasts over here, we get Black Powder Newsletter :thumbsup:

Too bad, you would have enjoyed this particular article. It's a very good one on just the subject you refer to.
But you know that you CAN get Muzzleblasts "over there":thumbsup:
It's only an additional $10 ($50 instead of $40) for a year's membership to the NMLRA if you are not in the USA. The sub to Muzzleblasts is part of it. Good stuff every issue by the "Bevel Brothers" and John Curry.
Jack

 

[Uncle Jed]

Would I willingly drop that gun 17 inches on to my shoulder?

We-e-e doggies, that sure would put a hurtin on ya.
Although I lacked sophistication a Squire Robin on these matters, seems to me this calculated number would only hold true if you were shooting straight up, then we would receive the full effect of this felt recoil. Since we shoot (for the most part) at right angles to our bodies, the effect is reduced because our spine flexes like a shock absorber on a new truck and dampened the felt recoil to an extent.
I know that the force exerts the same no matter which way the gun shoots, but the way our body reacts to it depends on our posture at the time the weapon is fired.

 

[robinghewitt]

seems to me this calculated number would only hold true if you were shooting straight up, then we would receive the full effect of this felt recoil.

Straight up recoil? That sounds like an excuse to post my wallgun clay shooting movie, yet again

wall clay movie 1.8 Mb

Well, there might be someone who hasn't seen it yet :crackup:

 

[arilar]

Robin,
Havent seen it before ::. Great stuff :applause:!!
ARILAR :: :thumbsup:

 

[Boer]

The weight of the powder charge would have to be brought into Robin's calculations as well. Things like stock shape makes recoil very subjective.

 

[robinghewitt]

Robin,
Havent seen it before ::. Great stuff :applause:!!
ARILAR :: :thumbsup:

I think I'll use it as my signature :thumbsup:

 

[Stumpkiller]

Ah, Stumpy puts on his alchemist's hat.

The powder doesn't weigh anything by the time it leaves the muzzle , but instead has been reconverted to elements (air, fire, and earth). In fact, the smoke rises because it is lighter than air, so it has a negative weight. :haha: The mass has been converted to energy, gas and fouling. We know energy is without weight. You can prove this because a lightbulb weighs the same on or off, and a discharged battery weighs as much as a fully charged one. The gas, we demonstrated, has negative weight. The fouling doesn't weigh much, but it is a mess.

Otherwise, they would have designed firelocks with the vent at the forward end of the powder charge so that the recoil would have been reduced. ::

Have I scared ye, yet?

 

[Mike Brooks]

Here's my theory on recoil. #1 if it hurts when you pull the trigger it ain't fun. :cry: If it ain't fun it's time to look for somethingf else to do.Chances are you have too much gun for what you're shooting at. If you're actually hunting game that will eat/kill you and have to have a gun with monumental recoil than you better head to a man that makes stocks for a living and have that gun fit to you, it will make a very painfull situation more bearable.
I'm not a fan of guns with recoil. I can shoot a 12 ga. or a 30.06 all day if the stock fits properly, but if I come across a gun that hurts me it's headed on down the road to somebody else that thinks pain is cool. eace:
Recoil that causes pain makes the shooter anticipate the shot and also develops one hellofa flinch, both or which are not conducive to accurate shooting. :shake:

 

Actually the weight of the charge, wad, etc. or as it is commonly called by ballisticians the "ejecta", is figured into the ballisticians formula for recoil.........

The formula used for recoil calculations are:
RI=(BM*BV+PC*CM)/g*mcoef - for Recoil Impulse;
RV=g*RI/GM - for Recoil Velocity;
RE=GM*RV2/(2*g) - for Recoil Energy;

BM is bullet mass in grains or grams, BM > 0;*
BV is the bullet muzzle velocity in ft/sec or m/sec, BV > 0;*
GM is the gun mass in lb or kg, GM > 0;*
CM is the charge mass in grains or grams, CM > 0;* g is the gravitational constant, 32.17 or 9.81;
PC is the powder gas effective escape velocity constant, that equals 4000 (1220 for Metric) for smokeless powders and 2000 (610 for Metric) for blackpowders;
mcoef is 7000(number of grains in lb) for English system & 1000 for Metric system.
* - Only first two decimal digits are used.

A handy to use recoil calculator for both shotguns and rifles can be found here
http://zknives.com/bali/index.shtml
The above quote is borrowed from that site........

"Actual" recoil will be the same in any gun of the same weight using the exact same exact load. Whereas "perceived" or felt recoil also factors in the guns shape - a straight stocked rifle with a wide, flat "shotgun" buttplate generally (all things considered)has less perceived recoil than a gun with a big drop in the stock and a narrow curved "rifle" buttplate. A good example is the Winchester lever action in 30-30 - it often has more perceived recoil than a well stocked bolt action firing a heavier loaded 30-06 - reason the stock shape. Like Mike said if it fits wrong it's going to hurt no matter what....

For example - One of the most "viciously" recoiling rifles I've ever fired is a Winchester 95 in 405 Winchester! :shocking: :curse: :shocking: bent stock and that curved buttplate are plain murder
On the other hand I've fired several different "elephant" guns with fairly straight stocks and a wide flat buttplate, all the way up to 577 Nitro (and 8 bore in blackpowder) and while "not fun" by any means they were not "vicious". of course there's a point of no return when you get into the big bruisers...

IIRC - the US Militry once did a quantitative study on recoil energy and found that once it reached above 16-18 pounds free recoil the cumulative effects became counter productive to good marksmanship. Note that the 30-06 service round generates about 17 lbs recoil in the military rifles in that caliber...........

 

[robinghewitt]

The formula used for recoil calculations are:
RI=(BM*BV+PC*CM)/g*mcoef - for Recoil Impulse;
RV=g*RI/GM - for Recoil Velocity;
RE=GM*RV2/(2*g) - for Recoil Energy;

Blooming heck. It was just a bit of fun

OTOH, this is gobbledegook, it means nothing. Dropping the gun 17", now that I can understand :thumbsup:

 

[BS]

http://sst.benchrest.com/recoil.html

 

[Gaze]

Blooming heck. It was just a bit of fun

OTOH, this is gobbledegook, it means nothing. Dropping the gun 17", now that I can understand :thumbsup:

Here's a fun experiment. Hold the gun about one inch or more from your shoulder and pull the tigger. I did that pheasant hunting with a 16g.

If one holds the gun firmly against his shoulder, then shoulder and the gun should be one and the same. Thus Bluto would experience less recoil then Olive Oil. :m2c:

 

[scott k]

and a discharged battery weighs as much as a fully charged one.

Just a ?, When you check a battery electrolyte with the little ball thing you are checking the specific gravity of the liquid. A battery that is discharging is turning the acid (sulfuric) into water.
a gallon of water weighs 8.3454 pounds per gallon with a s.g. of 1.0. Sulfuric acid weighs between 10.79to 15.2 per gallon depending on the concentration of it with a s.g of 1.3 to 1.4.
Why doesn't the battery with water in it(discharged) weigh less. :huh:
Lehigh...

 

[Stumpkiller]

Outgassing Hydrogen does occur in a lead-acid battery. If you've slagged a battery enough to convert the acid to water it will have accretions of sulphur oxides on the lead plates (or in the sump area of the case) and the weight is still in the battery.

But mine is a sealed "maintenance free" battery. :winking: Or a NiCad flashlight cell. Or a Mercury watch battery.

Back to the recoil:

There are some guns that have a "satisfying" level of recoil. A 30-40 Krag, a 270 Win, an eight pound .50 muzzleloader, a nine pound .54, etc. Not enough to knock your retinas loose, but enough to be life affirming.

Part of the whole menu of savory sensations of shooting. The acid & sulphur smell of the smoke, the "BANG", the kick. Just lobbin lead at 100 or 200 yards at cans and sod clumps for the sheer joy of shooting.

There's only three kinds of recoil: hardly any, pleasant, too much. Why try and measure it any farther?

One of the absolute most unpleasant guns I own is a 10" barrel .22 Hornet for a Contender. Negligible recoil, but the muzzle blast is as bad as my .338 Win was! The flash and bang is absolutely painful. From such a piddly little cartridge! The problem is that IMR 4227 is THE .22 Hornet powder, and it seems a large percentage of it ignites at or just past the muzzle. I will not shoot this gun without ear protectors, so it is a failure as a woodchuck gun.

Now, the long discontinued 10" octagonal .44 Mag barrel that is only 5/8" across the flats at the muzzle (that only leaves about 1/10" of metal around the bore!) is a recoil nightmare in the Contender. A real wrist breaker.