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Recoil 101
#1
Recoil 101

Posted By: ML - Registered User

Posts: 308

Posted At: (6/25/02 11:03 am)

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When Push Comes To Shove: Calculating Recoil



There’s a very instructive post over in the "For Sale" section of this Forum, and I’m going to reproduce it (with only minor edits) here: The posting party is Riddlin, a long-time member of this Forum.



(Quote)

"I spent most of last year working at a couple of guest ranches and an outfitter in the Shoshone National Forest outside of Cody, Wyoming. Lots of big cuddly bears in that neck of the woods. I had with me a Marlin 1895 Cowboy model .45-70 . . . [and bought] some Garrett 540-grain Super-Hard Cast Gas-Checked Hammerhead [cartridges loaded at] 1550 FPS. . . so the box said.



"I went out to a range to let a few fly before hunting camp. Well I will recount this only for educational purposes. I fired one (1) round through the Cowboy and said ‘Goddamn boys that’s enough!’ It literally jarred my teeth. I wanted no more. We always joked in the Corps about firing the Barrett 82A1 50 without a muzzle brake; well now I feel I have just a little idea how bad it might be."

(End of quote)



Here we have a working cowboy/outfitter and former United States Marine who’s drawn the line concerning recoil, and admitting that even he has his limits given a specific firearm/cartridge combination! And by doing so, he’s done all of us a great favor. At some point, depending on the individual, firearm, and chambering, you’ve got to say enough--it just doesn’t make any sense any more, and you’re not going to be an effective shot. Any professional will tell you he’d rather work with a hunter who shoots a standard caliber well than a greenhorn who shows up with a light a super magnum he can’t shoot well due to excessive recoil.



Now I thought Our Contributor Riddlin, if he’s recovered his vision yet, might be interested in knowing just how much punishment he altruistically sucked up in the cause of our enlightenment, so I warmed up the calculator and ran some numbers, calculating the free recoil of his hot Garrett .45-70 load in that particular rifle.



But first, an aside. Many variables go into determining how much of a beating you take or don’t take from a firearm. With rifles and shotguns, stock design is a significant factor, but tough to quantify. The closest we can come to a scientific number is something called Free Recoil Energy, expressed in foot-pounds. Basically, this is force generated were the firearm suspended by strings or wires and allowed to recoil backward freely. While not perfect, it’s an instructive comparison.



The formula for calculating Free Recoil requires one to know the weight of the rifle or shotgun, the weight of the bullet or shot load, the weight of the powder, and the muzzle velocity. A formula appears as an appendix to this post.



Back in 1873 when Uncle Sam developed the .45-70 Government cartridge in the "Trapdoor" Springfield, the standard load was a 405-grain bullet propelled to 1320 feet per second by 70 grains of black powder, this launched by a 9.21-pound rifle. Cavalry troopers of the era were armed with a 7.9-pound carbine, and the recoil from the full-house rifle load was deemed too stout for these hardy souls in the lighter gun, so they were issued a 405-grain load propelled at 1150 feet per second by 55 grains of black powder.



Contributor Riddlin’s Marlin Model 1895CB "Cowboy" lever action weighs eight pounds (for all intents identical to the Cavalry’s Trapdoor Carbine) and hucks that 540-grain slug out the muzzle at 1550 feet per second.



Free Recoil Energy



Trapdoor Rifle, .45-70-405 at 1320 fps=

15.42 foot-pounds



Trapdoor Carbine, .45-55-405 at 1150 fps=

12.86 foot-pounds



And how much energy did our man in Wyoming absorb in the cause of our enlightenment?



Marlin M1895CB, .45-70-540 at 1550 fps=

43.90 foot-pounds



Buy that man a beer.



That’s almost three and a half times what the government thought a hardened cavalry trooper of the last century could absorb regularly.



Those Garretts are superb cartridges, offered by enthusiast craftsmen who are doing non-handloading shooters a great service. But they do exact a price.



The greatest lesson here, to my thinking, is that one should hesitate before one rushes out and plunks down a big wad of cash for a large-caliber magnum. Shoot a couple of hundred rounds out of a .30-’06, a .308, a .270, or even a .30-30 before you decide you really need more. If you do, and you can shoot it well, congratulations. By all means, use enough gun--just don’t handicap yourself with too much.



Best regards, and thanks to Mr. Riddlin again,



--ML



25.vi.2



Calculating Free Recoil Energy (from Fr. Frog’s website)



Supply the following numbers, and have at it.



WG = Weight of gun in pounds

WB = Weight of bullet in grains

WP = Weight of powder charge in grains

VB = Muzzle velocity of bullet in f/s

I = Interim number (Recoil Impulse in lb/sec)

VG = Recoil velocity of gun (f/s)

EG = Recoil energy of gun (ft-lb)



I = [(WB * VB) + (WP * 4000)] / 225218



VG = 32.2 * (I / WG)



EG = (WG * VG * VG) / 64.4



Notes: The "4000" is the nominal velocity of the powder gases for commercial smokeless powder. It is sometimes stated as 4700 in some sources. You can try it with both values to see the effect of the different numbers. If you are doing these calculations for a black powder load use 2000.









Edited by: ML at: 6/25/02 12:12:42 pm





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Excellent information & painful

Posted By: Brother Dan - Registered User

Posts: 81

Posted At: (6/25/02 11:51 am)

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You can know yourself only when the mind is open, unprepared to meet the unknown. - J. Krishnamurti





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Awesome! That was very informative! Thanks

Posted By: David R - Registered User

Posts: 123

Posted At: (6/26/02 9:52 am)

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Re: Recoil 101

Posted By: Mountain Goat - Registered User

Posts: 359

Posted At: (6/28/02 4:01 am)

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ML great post but.......

There are other contributing factors to felt recoil. The design of the stock has a great deal to do with what the end user "feels" The fit, drop at the heal, and energy absorbtion device aka recoil pad all contribute to the reduction or amplification of felt recoil. I recently got a 6.2 lbs rifle in 300 WSM (that included scope) During the purchase process I had a long discussion with the manufacturer about recoil and weight. He convinced me that there due to stock design, composition, etc that the felt recoil would be manageable (he had designed a stock that produced a recoil impulse straighter back into the shooter instead of up (rotational) and the butt of the stock was wider with a thick efficient pad. What I found was a nice rifle that had an extremely quick recoil that I could not manage. I shot it 20 times with factory loads in a number of positions and finally excerised his garantee and returned the gun and went with a .257 Roberts. Much more manageable. Mind you a hunt with a .338 Win Mag and shoot a 50 cal and 45-70's regularly but could not manage the speed and volume of recoil from a ultra light rifle. I would say that the stock design did substantially help but not enough.



Oops rambling again

Take Care

Pat





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Re: Recoil 101

Posted By: Birdog - Registered User

Posts: 1300

Posted At: (6/28/02 5:14 am)

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Another thing you will want to consider if you are shooting a large caliber rifle, with a scope, is eye relief!



I hade a Rugar M-77, 7mm Magnum, with a Leupold 3X9 scope. The scope had a 3" eye relief, and when bench shooting, it was fine.



I was out hunting and a couple of Bucks burst from the trees, so I made a quick shot from a standing position. I neglected to have a tight hold against my shoulder, and wound up with a nice moon shape gash across the top of my nose. I still have a deep groove in the bone where the scope hit me. It was at least 15 minutes before my vision cleared and I had blood all over my face. It affected my shooting for a long time after that.
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"In the school of the woods there is no graduation day" Horace Kephart


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