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Thread: Recoil Energy

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    Member Nukalpiaq's Avatar
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    Default Recoil Energy

    On the subject of recoil, what formula is used to determine it? For example; I have read that a 358 Norma Magnum rifle weighing 8.5 lbs shooting a 250 grain bullet @ (MV) 2799 fps & (ME) 4350 ft. lbs generates 35 ft. lbs. of recoil energy. I would like to learn how to compare various calibers suchas; 358 NM vs 338 Win Mag, 375 Ruger vs 375 H&H, 358 Naki vs 358 Norma Magnum, etc.
    I think that recoil is a deciding factor for some shooters when selecting rifles and cartridges. Knowing how to make accurate estimates on felt recoil may help when making decisions on which rifle to buy and cartridges to use. Thanks

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    Recoil is calculated in three aspects.

    Recoil Impulse (RI), Recoil velocity (RV) and Recoil Energy (RE). For best results, in that order.


    RI=(Bw*Bv) + (Pw*4400)/225190 - lbs/sec

    RV=RI*32.17/Gw - ft/sec

    RE=Gw*RV(squared)/64.34 - ft lbs

    Bw=Bullet weight in grains.
    Bv= Bullet velocity in ft/sec.
    Pw=Powder weight in grains
    Gw=Gun weight in pounds

    4400 is the constant which represents the exit velocity of the powder gasses. (a major part of recoil, I call it the Bill Lear effect) This number has variably been used from 4200-4700 fps. I believe it does vary but it isn't measurable without good instrumentation.

    225190 is the acceleration of gravity (g) 32.17 ft/sec*7000(the number of grains in a pound) This constant gets it back to common units.

    g=32.17 ft/sec

    g2=64.34 ft/sec

    This will provide a close approximation of recoil. We are generally interested in Recoil Energy and Recoil velocity.

    A 375 with a 300 grain bullet and 80 grains of powder which gives 2600 fps velocity in an eight pound rifle will produce about 50 ft lbs of RE and an RV of 20 fps.

    Generally calibers that produce the same ME from the same weight of gun will be equal. But where large differences in powder charge produce the energy level, the higher powder charge will produce more recoil An example of this is the 416 Rigby vs the 416 Remington. The Rigby kicks more with it's greater powder charge.

    Have fun.
    Last edited by Murphy; 06-02-2009 at 08:49.
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    New member George's Avatar
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    Default or if lazy


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    Thanks for the mini-lesson Murphy...I'm always learning from you professor. Nice link George...thanks...and with Murphy's lesson I understand the interrelationship between the variables as I input them.

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    Thanks, I have always been curious how recoil was determined.

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    Default Still Puzzled

    "Generally calibers that produce the same ME from the same weight of gun will be equal. But where large differences in powder charge produce the energy level, the higher powder charge will produce more recoil An example of this is the 416 Rigby vs the 416 Remington. The Rigby kicks more with it's greater powder charge."


    If we assume two rifles of different caliber but with equal mass, and two bullets of equal mass, exiting the muzzle at equal velocity, I have never understood why the mass of the powder charge would be relevant. Is this some kind of "Jet exhaust" phenomenon, i.e. more powder = greater volume of expanding gasses pushing back on the bolt head for a longer period of time after the bullet has exited the barrel?

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    Quote Originally Posted by Sako Workhorse View Post
    "Generally calibers that produce the same ME from the same weight of gun will be equal. But where large differences in powder charge produce the energy level, the higher powder charge will produce more recoil An example of this is the 416 Rigby vs the 416 Remington. The Rigby kicks more with it's greater powder charge."


    If we assume two rifles of different caliber but with equal mass, and two bullets of equal mass, exiting the muzzle at equal velocity, I have never understood why the mass of the powder charge would be relevant. Is this some kind of "Jet exhaust" phenomenon, i.e. more powder = greater volume of expanding gasses pushing back on the bolt head for a longer period of time after the bullet has exited the barrel?

    Eggzaakly!
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    What goes in, must come out. That gas is also moving ~5200fps, so it is substantial.
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    Just don't forget ergonomics.

    An 7 pound rifle with a good stock design with proper drop at comb and heel and proper cast and soft recoil pad will feel so much better than a poor designed rifle even if the poor design rifle is 10 pounds and has less recoil.

    I can shoot my .375 quite comfortably for 40 rounds...my friends FR8 Mauser in .308 brings tears to my eyes after 3 rounds cause it just don't fit me at all.

    It is actual recoil vs. felt recoil.

    jedi

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    Default Stock design

    Just wondering what folks consider is the best stock design for reducing felt recoil ? I have always leaned toward classic style designs. With my 2 McMillan classic stocks the only input I provided for proper fit is LOP selection. Everything else like drop @ comb and heel and cast is never discussed. I have always assumed that these other design features have already been built into that particular style of stock. On my next stock I think I wil ask a few additional questions. Thanks

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    Quote Originally Posted by Nukalpiaq View Post
    Just wondering what folks consider is the best stock design for reducing felt recoil ? I have always leaned toward classic style designs. With my 2 McMillan classic stocks the only input I provided for proper fit is LOP selection. Everything else like drop @ comb and heel and cast is never discussed. I have always assumed that these other design features have already been built into that particular style of stock. On my next stock I think I wil ask a few additional questions. Thanks
    Depends on many factors like rifle weight, primary sights whether scope or irons and recoil pounds and recoil velocity of the rifle.

    Grip style plays a role too as well as sling stud placement.

    Straighter grips are better for heavy recoiling rifles to keep your second finger away from getting bruised by the trigger guard.

    The same heavy recoiling rifles place studs on barrels away from the off hand for the same reason.

    cast on and cast off help with sight speed alignment as does drop at comb and drop controls or induces rise from recoil.

    jedi

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    Quote Originally Posted by Doc View Post
    Thanks for the mini-lesson Murphy...I'm always learning from you professor. Nice link George...thanks...and with Murphy's lesson I understand the interrelationship between the variables as I input them.
    Ditto. Archived on disk.

    Thx,
    Brian

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    Quote Originally Posted by Murphy View Post
    Eggzaakly!
    I read once that recoil occurs to a great extent from the gases pushing back on the end of the barrel as the bullet comes out, and that's why compensators and porting work ...they allow the gas to escape in bite sized pieces rather than all at once on the end of the barrel. I wonder if machining the end of the barrel into a cone shape (obviously with a hole in place of the cone's point) would result in lower recoil by letting the gases blow backward more easily? Anyone? Murphy?

    Brian

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    Default Muzzle Cone?

    "I read once that recoil occurs to a great extent from the gases pushing back on the end of the barrel as the bullet comes out, and that's why compensators and porting work ...they allow the gas to escape in bite sized pieces rather than all at once on the end of the barrel. I wonder if machining the end of the barrel into a cone shape (obviously with a hole in place of the cone's point) would result in lower recoil by letting the gases blow backward more easily? Anyone? Murphy?"

    I don't think that would work. I think essentially 100% of the recoil force is on the bolt face, not on the end of the muzzle where gasses would be expanding primarily straight forward. Only the tiniest % would be blasting back toward the shooter, which is how I understand the way porting works -- Look out behind and beside!

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    Quote Originally Posted by Sako Workhorse View Post
    "I read once that recoil occurs to a great extent from the gases pushing back on the end of the barrel as the bullet comes out, and that's why compensators and porting work ...they allow the gas to escape in bite sized pieces rather than all at once on the end of the barrel. I wonder if machining the end of the barrel into a cone shape (obviously with a hole in place of the cone's point) would result in lower recoil by letting the gases blow backward more easily? Anyone? Murphy?"

    I don't think that would work. I think essentially 100% of the recoil force is on the bolt face, not on the end of the muzzle where gasses would be expanding primarily straight forward. Only the tiniest % would be blasting back toward the shooter, which is how I understand the way porting works -- Look out behind and beside!
    Oh, yes. The escape of the high pressure gasses is very much a part of the recoil of any rifle. I have written about this many times and refer to it as the Bill Lear effect, or "jet propulsion" effect some have said it is the same as rocket thrust and that is true. The powder charge relates to the volume of the gas and powder charge and gas volume go up proportionally. The exit velocity varies and has been measured at velocity from 4100 to over 5000 fps. It is typically from 15,000 to 30,000 psi at the muzzle and can give quite a shove. Very definately part of felt recoil. In some rifles it is has much as half the felt recoil.
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    Default "Lear Effect"

    I'm not disagreeing with the jet propulsion effect, only where that force is transferred to the rifle so that someplace down the road the shooter feels it as recoil. Force from the expanding gasses after the bullet has exited the muzzle would be transferred to the walls of the bore, the walls of the chamber, the bolt face, the air, and to the tip of the muzzle. Force exerted on the walls of the bore and the chamber would not be felt at all by the shooter as recoil, since their vector would be outward, not backward. Just as with a rocket, the "recoil" force which propels the rocket is exactly opposite the vector of the rapidly expanding gasses, and it is exerted on the sealed end of the combustion chamber (in this case, the bolt face). Once having exited the muzzle, the gasses are no longer contained and are therefore free to expand in all directions, creating the "bang." The fact that we sometimes see carbon build up on the outer face of the muzzle shows that some gasses are hitting it, but without containment, I doubt it could compare with the backward force on the bolt face.

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    I know we often like to debate various mesurements in gunnery, ie KE, sd, recoil pulse etc, but what's more important is answering the underlying question. In the case of KE, sd et al, the real question is will this bullet kill the animal I plan to hunt. With the recoil measurements, the real question is can I shoot the gun without the recoil being detrimental to my ability to shoot it.

    I've shot enough chamberings to have formed some conclusions, and I think they hold true for the average shooter, ie those that don't suffer from physical ailments that will affect their ability to deal with recoil i.e. neck and shoulder problems. I put chamberings into classes:

    223 and below, you can shoot them all day long without the recoil bothering you.

    243-30-06 these rounds require a good stock but can be shot from any position and merely require a bit of practice.

    338-375, with a good stock, and reasonable weight 7-8#'s minimum, they can be shot from any position and won't hurt you. But, they generate enough recoil to cause flinching in an inexperienced shooter and aren't something you'll shoot all day long, though 40-50 rounds is no big deal.

    416 and above can really slap the un-initiated and require a serious comitment to master.

    458 lott and above can cause serious harm, and generate enough recoil that every shot requires some serious concentration before squezing off a shot, unless one makes the gun so heavy as to be impracticle in the field, or resorts to a muzzlebreak.

    The 458 lott was a great educator to me as to what I could handle recoil wise. I never flinched or was hurt by either of them, but I also never burned more than 10 rounds in an hour shooting session, and sometimes less than that. I could also pick up a .308 and it literally felt recoil-less in comparison.

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    Quote Originally Posted by Sako Workhorse View Post
    I'm not disagreeing with the jet propulsion effect, only where that force is transferred to the rifle so that someplace down the road the shooter feels it as recoil. Force from the expanding gasses after the bullet has exited the muzzle would be transferred to the walls of the bore, the walls of the chamber, the bolt face, the air, and to the tip of the muzzle. Force exerted on the walls of the bore and the chamber would not be felt at all by the shooter as recoil, since their vector would be outward, not backward. Just as with a rocket, the "recoil" force which propels the rocket is exactly opposite the vector of the rapidly expanding gasses, and it is exerted on the sealed end of the combustion chamber (in this case, the bolt face). Once having exited the muzzle, the gasses are no longer contained and are therefore free to expand in all directions, creating the "bang." The fact that we sometimes see carbon build up on the outer face of the muzzle shows that some gasses are hitting it, but without containment, I doubt it could compare with the backward force on the bolt face.
    So what are you disagreeing with? We did put a man on the moon back in 1969 with the thrust principle. The rocket suspended in space will be moved away from the escaping gas of the rocket motor or an aircraft in flight will be moved by the escaping hot exhaust of the Pratt & Whitney jet engine and a rifle will be moved rearward against the shoulder of the shooter by the hot escaping high pressure gas. This gas pressure is approximately 20,000 psi.

    If you don't think it has an affect, hook the air hose up to your compressor. Run it up to about 150 psi, lay it on the ground and cut the fitting off the end with an axe. If the hose just lies there and doesn't move, I'll remove the powder charge and escape velocity from my formula, and I'll go back to the University of Missouri, Rolla and ask them to change everything they taught me about physics and I'll forget everything I've been studying about gas propulsion for the past 30 years.

    You may not be able to feel the difference on your shoulder when varying the powder charge by a few grains but it is in fact a legitimate part of the recoil of any single stroke thermo-dynamic device.

    Please don't tell me how the "bang" is created or that gravity has nothing to do with bullet drop. I can't take that much regection.
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    Remember way back when, when TananaBrian asked "I wonder if machining the end of the barrel into a cone shape (obviously with a hole in place of the cone's point) would result in lower recoil by letting the gases blow backward more easily? Anyone? Murphy?"

    My point was, I don't think the shape of the end of the muzzle is going to measurably affect the amount of recoil. I do agree that rockets work by "jet propulsion," but they have to work by the jet propulsion pushing against some part of the vehicle, and in my opinion, it isn't the outermost tip of the burn orifice that the force is being applied to. It is the closed end that all that expanding gas pushes against.

    In the example of the air hose with the 150 lbs of pressure in it, cut off both ends at once so the expanding gas has no part of the hose to push against, and you may see some drammatic flailing about, but the net movement of the hose should be zero. Cut off both ends of a cannon and fire it and you get lots of jetting, but no recoil, because no closed end for the gasses to push against. (Warning: Do Not Try This At Home!)

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    Sako,

    I agree, if the shape of the end of the muzzly has any efffect I don't know what it would be. I don't know what Brian was getting at but I do know physics and I do know what makes recoil and I think if you cut both ends of the hose the hose (both ends) will move for a very brief time until the small charge of pressure vents off. A lot of people have trouble grasping the "thrust" created by escaping gas. It doesn't have to push on anything, it is the difference in pressure that cause the rifle to move away from a higher pressure. If it had no effect tell me what makes an airplane fly (lift) if it isn't this difference in pressure? Very slight difference in pressure from the top of the wing to the bottom (less than one psi) creates the lift which "moves" the plane upward. Pressure differential is stored energy and as it is released it pushes the object, which contains mass, away from the exit point. Rockets, jets, RPGs, ruptured air hoses, etc. Does that help?
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