Peak pressure and recoil profile

Discussion in 'Firearms & Ammunition' started by Rick Hill, Oct 3, 2016.

  1. Rick Hill

    Rick Hill AH Senior Member

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    I understand that total recoil is the sum of the work needed to accelerate a bullet say 400 Gr to 2400 fps and also the "jet" effect of the gases. So a 416 Remington Magnum burns less powder than a 416 Rigby and the "total" recoil is lower BUT isn't the recoil profile more like a slap than a shove as the peak pressures are much higher (I am asking)? With all the bright people on this forum is there anyone who has looked at recoil profiles of force versus time? It just seems intuitively there would be a large spike initially with high operating pressures? Or faster burning powders? It also seems like a push from a friend is better than a punch or a slap of similar total energy.

    Rick Hill
     

  2. Ray B

    Ray B AH Elite

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    While the bullet is in the barrel, the balance point of the rifle will determine the rifles location- that is to say: if you balanced the rifle with the bullet in the chamber there is a point where half the weight is in front and half behind that point. When fired the bullet and powder (in the form of gas) moves forward. If you were able to rebalance the rifle when the bullet was at the muzzle, but still in the barrel, the balance point would have moved forward a slight amount. The position of the bullet as it went from leade to muzzle would indicate the shift in balance point. With faster powders the bullet would be moving quicker so relative to the slower powders the initial movement of the rifle would be more, but with slower powders, as long as the total time in bore is the same, the balance point would be the same. So figure out the two balance points, calculate the time in bore for the bullet and you'll see what the initial rate of recoil is. then the bullet exits and the slower burning powder would have higher pressure, so the jet effect of the pressure is in addition to the in-bore recoil.
     

  3. mark-hunter

    mark-hunter AH Elite

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    Ray B, as I am very sensitive on recoil, this subject is very interesting to me!

    So far, I kept to the theory that 10 percent increase in rifle weight will keep recoil 10% down, and reduction of bullet weight by 10% will keep recoil down by half - so down by 5%.
    (to reduce the recoil, to increase the rifle weight, and reduce the bullet weight... pure physics)

    However, I was never considering much the rifle balance.

    How would you define a well balanced rifle, which keeps recoil tame?

    Or, to put it in other words: in terms of recoil, what is a well balanced rifle?
     

  4. Rick Hill

    Rick Hill AH Senior Member

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    In terms of adding weight for recoil reduction, Tungsten (W; Wolfrum) rods 20 -22 mm in diameter and 100 mm long are available on ebay. Wolfrum is almost 50% more dense than mercury and I recently used it to tame a 6 lb rifle chambered in 405 Win (Ow). You can use the existing stock bolt hole or make one of your own. This easily adds over a pound and a half and makes Ow, Wow and I don't have to wonder about Mercury vapor or travel restrictions.

    Rick
     

  5. Ray B

    Ray B AH Elite

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    It isn't balance in the sense of being handy or ill-fitting. What I am saying is that in a closed system, which a rifle is prior to the bullet leaving the muzzle, the rifle will remain "balanced", So like a balance beam scale, as the bullet and the powder gas move forward in the barrel, the balance shifts slightly forward. The heavier the bullet, the farther forward the balance point shifts; the faster the bullet, the quicker the shift takes place. The total recoil is a function of the momentum, but two loads that result in the same momentum can have different forms- which is what you're saying about varying recoil. for example, #1 bullet weight 100 grains, muzzle velocity 3000 fps, with 24" base of bullet to muzzle, avg velocity in bore 1500fps, time in bore 1/750th second. #2 300 grain bullet, muzzle velocity 1000 fps, avg velocity 500 fps, time in bore 1/250th sec. So both bullets have the same momentum (basically a multiple of m x v) the balance point of the heavier bullet is farther, thus the gun moves more, but with the lighter bullet, even though it moves less distance, it get there three times faster. This is why some guns which have a lot of "foot pounds" of recoil are felt more as a push than a jab.
     

  6. Rick Hill

    Rick Hill AH Senior Member

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    OMG - a scientific argument to buy a 416 Remi and study it in comparison to my 416 Rig?? Is there anyone on the west coast that would like to pursue the measurements? I am reasonable close to Angeles Ranges (west of Cal Tech). Maybe we should all be running high pressure, moderate velocity bolt guns?

    Rick
     

  7. Grumulkin

    Grumulkin AH Veteran

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    Yes, the center of gravity moves forward by a slight amount. To figure out how slight, calculate as a percentage what the bullet/ejecta weight is compared to the rifle. And you REALLY think this has an effect on perceived recoil?

     

  8. mark-hunter

    mark-hunter AH Elite

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    This may sound logical, but I am starting to develop different way of thinking.
    The real question to be asked may be: In which part of barrel the bullet accelerates the most? And for how long?

    The thread subject is: Peak pressure and recoil profile.

    So, if the bullet exits with same velocity, but with different peak pressure profile in two different barrels of same length, with two different types of powder, then most probably the recoil will be softer in the barrel with more extended and prolonged pressure peak curve.

    Like the car: from o to 100 km/h in 6 seconds, or from 0 to 100 in ten seconds. The acceleration in in the second case will be more gentle on the driver, with the same speed achieved.
    Similar is with recoil I presume. Except that recoils happens in miliseconds, and we have no way of telling the difference in accelaration, except (possibly) by individually felt rifle kick.
     

  9. Grumulkin

    Grumulkin AH Veteran

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    I can go along with this. What I don't go along with is the whole bullet/ejecta center of gravity thing being a significant factor.
     

  10. Desperatezulu

    Desperatezulu AH Veteran

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    Yup, some flaky physics here to put it mildly! How does all this mumbo-jumbo centre of gravity cross balancing point explain what happens if the gun is mounted on a lead-sled and there is no tipping etc going on?:cool:

    Back on topic - simplistically, recoil is generally believed to be a combination of the pressure 'peak' (both the amplitude and wave length of the impulse has an effect), momentum and stock design.
    So a faster-burning powder builds pressure faster (all else being equal) and creates a pressure curve with a higher peak/amplitude. Which equates to a sharper punch of recoil.
    A low peak and long wave-length/frequency would be more a slow push and less of a punch.

    On momentum, the greater the combination of mass (bullet plus gases) * velocity, the greater the equal and opposite reaction, aka recoil. The higher the mass of the gun, the lower the recoil velocity.

    Then factor in stock design. And the inertia of the shooter (standing upright vs laying down prone).

    On the argument of 416 RM versus Rigby, the RM is something like 60k psi using a faster powder, versus the Rigby at 48k psi using a slow powder. The Rigby will have a greater mass of gas blasting out the barrel due to the greater powder charge but that extra 20grains will be difficult to perceive.

    I suspect that the identical mass gun and stock design plus the same bullet mass and velocity and the recoil difference between the two would be fairly small, maybe not even perceptible.
    In which case you choose the Rigby. Which was the answer before the physics lesson started! :LOL:

    EDIT: I was busy with my essay while Mark and Grumulkin were replying - apologies for repeating some of their message.
     

  11. Rick Hill

    Rick Hill AH Senior Member

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    If you look at Chuck Hawks recoil info the difference between 416 Rem Mag and 416 Rigby is not slight and almost 10%. This would be like adding a pound of weight to a 9 pound rifle. BUT if this is a 90% jab versus a 100% push, I would add the weight and take the push. It just seems amazing to me that we don't have this info. In general I do not like faster burning powders and velocities above 2500 fps BUT what is the science and what is the reason?

    Rick Hill


    .416 Rem. Mag. (400 at 2400)

    10.0 Lbs

    52.9 Recoil energy

    18.5 Recoil velocity


    .416 Rigby (400 at 2400)

    10.0 Lbs

    58.1 Recoil energy

    19.3 Recoil velocity
     

  12. Grumulkin

    Grumulkin AH Veteran

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    I believe the recoil velocity would be the same with added mass to the gun but more of the energy would be absorbed by the added mass; i.e., the buttstock would move as fast but not as far or, if you prefer, the shoulder wouldn't have to absorb as much of the energy.

    I believe that stock design is a huge factor in felt recoil.

    I agree that the difference in recoil between a 416 RM and a 416 Rigby would probably be difficult to perceive.
     

  13. PHOENIX PHIL

    PHOENIX PHIL AH ENABLER AH Ambassador

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    Respectfully, I would have to disagree with that due to conservation of energy.

    If the energy is the same between two rifles shooting the same load, the heavier rifle will have less recoil velocity.

    1/2 * m1 * v1 * v1 = 1/2 * m2 * v2 * v2

    If the mass (m2) is greater than mass (m1), then for the energies to be the same, velocity (v2) must be less than velocity (v1).
     

  14. Grumulkin

    Grumulkin AH Veteran

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    I can't argue with that.
     

  15. Ray B

    Ray B AH Elite

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    Pearls before swine.
     

  16. edward

    edward GOLD SUPPORTER AH Legend

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    it seems to me that felt recoil,how much ever is either handled or not,period.
     

  17. ChrisG

    ChrisG AH Fanatic

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    Typically speaking, recoil is a function of a huge number of things. To accurately determine recoil, you would need to have a huge amount of info but it can be reasonbly calculated via calculators. The only things it can possibly be a function of are: bullet weight, bullet velocity, powder weight, mass of air in the barrel in front of the bullet (small but there) and gas exit velocity. The last one is not as significant as the others but it would be important in say, a shorter rifle barrel where pressure is still very high by the time the bullet leaves the barrel. Conservation of Energy has problems with it when figuring recoil because energy can be dissipated in a plethora of different ways, Barrel heat, friction, shockwave as the gas exits the barrel, heating the air in front of the bullet via supersonic shockwave (assuming bullet is supersonic.) Conservation of momentum would be the best way for the average person without a lot of Newtonian and Fluid Dynamics calculations or software, to determine relative recoil. It goes something like this:

    If you just want to see my honest opinion, skip all the math and read the last paragraph.
    Momentum(p)=M*V, Let's say we have a 9.5lb gun and a 400 grain bullet with 90 grains of powder propelling it to 2,400 fps

    p(bullet)=(400/7000)lbs + (90/7000)*2400f/s
    p(bullet=0.0700lbs*2400f/s= 168lb*ft/s

    So p(rifle) has to equal p(bullet)

    p(rifle) = 168lb*ft/s
    168lb*ft/s = 9.5lb*V(rifle)
    (168lb*ft/s)/9.5 = V(rifle)
    V(rifle)=17.684 f/s

    Using this we can determine that the recoil energy of the rifle:

    e=1/2MV(rifle)^2 with M being 9.5lbs/32f/s(gravity)
    e=(.5)(0.297slug)(17.684f/s)^2
    e=46.439ft*lbs

    This is very simplistic because it doesn't take into account the rocket effect as it changes depending on how much pressure is left at the muzzle and the mass of the gas being expelled. But it gets you the recoil on a closed system. the rocket effect will typically add between 25%-35% to the total recoil depending on several factors. I am not going to get into all the calculations for rocket exhaust velocity and such because people are probably sick of reading my post as it is.

    So I say all that to say that the pressure spike is not going to have an appreciable difference in the felt recoil. Time in the bore and exhaust velocity are what will determine if it is a sharp smack or a push BUT... I have a feeling that you aren't going to notice a difference between an impulse that last .0015 seconds and one that lasts .0022 seconds. It is my opinion that recoil velocity, stock design, recoil pad design and the clothes you are wearing at the time you shoot are going to have a much more drastic effect on percieved recoil than any sudden spike in pressure. I know there are a huge number of calculations left out but... most people don't care about the math... I just love it!
     

  18. Pheroze

    Pheroze AH ENABLER AH Legend

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    ^^ :sleep:;)

    Seriously, I actually am fascinated by this discussion but I don't have the intellectual capacity to follow it properly. I do have an observation: it seems to me that bigger fellas feel the recoil more than little guys/gals. So, perceived recoil could also involve the speed or the shooter away from the force?
     

  19. Rick Hill

    Rick Hill AH Senior Member

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    Chris - OK so I am going to out you as an engineer! It's OK though my Dad is one and I recognize your type and have been trained in your ways! Go to U-tube and look up a video called "the knack". I think the problem is more complex and has to do with the rate at which the work is being done. This must have a very sharp initial spike with exponential decay for the Remi and a more gradual build and decay for the Rig. I know my rifles that operate at high pressures are more annoying to shoot. Now to measure this or try it out is the question. My 416 Rigby gets out of 10 day cooling off in 2 hours and 4 minutes. Anyone have a 416 Remi and lives within driving range of LA?

    Rick Hill
     
    ChrisG likes this.

  20. Buckdog

    Buckdog AH Enthusiast

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    ok i own 416RM and have shot friends 416rigby and we both say my 416RM whacks more, hows that for some science! unscientificalls the rcoil in my 416RM is sharper and faster rigby more big push. but who cares in the end we each love our guns and they are just the perfect recoil to us
     

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