Do cartridge case dimensions affect recoil?

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by Varminator 911, Nov 17, 2010.

  1. Varminator 911

    Varminator 911 Well-Known Member

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    I was recently having a good natured discussion on another thread about whether cartridge case dimensions affect recoil. I don't think so but I've been wrong before. So educate me if I'm wrong.

    My impression is that recoil is dependent on rifle weight, bullet weight and velocity, and weight of powder charge. There could be other minor factors affecting recoil but cartridge dimensions is not one of them.

    The other view expressed, as I understand it, is that if all other things are equal, a short fat case will have more recoil than a long thin case. Reason being that the short fat case has a larger case head. Thus with equal psi the force pushing back on the bolt is greater. Thus greater recoil.

    I feel that until the bullet leaves the bore, pressure in the case is pushing equally in all directions, including the base of the bullet, and these forces, fore and aft, cancel out. After the bullet leaves the bore the jet effect of escaping gases greatly affects recoil. But prior to the bullet leaving the bore internal forces don't affect recoil.

    What do you guys think?
     
  2. jcoop

    jcoop Well-Known Member

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    I am with you. I believe cartridge dia. can affect bolt thrust but bolt thrust is not the same a recoil. Recoil is from the bullet going one way and the rifle going the other. Simple as that right? The heavier the bullet and powder charge the more recoil you will get. Pushing a bullet faster will increase recoil. The lighter the rifle the more recoil you will get. I think they were over thinking it a bit.
     

  3. ovastafford

    ovastafford Well-Known Member

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    I am with you as far as the heavier the bullet the more recoil, more powder more recoil, etc....... I believe there is a difference in the felt recoil between a 300 wsm and 300 win mag. Both are pretty similar with about the same performance. The short mags recoil is more of a sharp quick punch to the shoulder compared to the 300 win mag which seems that the recoil isnt quite as sharp but a longer drawn out kick. Its hard to explain, but thats the experience I have had comparing the short mags to their longer brothers.
     
  4. DMCI

    DMCI Well-Known Member

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    A very excellent question for a sophmore physics student. You have a good intuitive feel for the question, but like many average Americans, damn little science to back it up.

    Energy is for a moving body is defined as E = 1/2 M V^2. The up arrow for purpose here will mean to the power of. The equation therefore is 1/2 Mass times Velocity squared. Mass is actually Weight/g, where g is the earth gravitation constant in english units of about 32.2 f/sec^2. E1 is generated by firing bullet and powder out the barrel

    Ok.

    So bullet, powder leave the barrel at great speed. This generates a reaction equal and opposite which can be the recoil.

    E2 is the reaction of the gun and is equal to E1. (According to Newton's third law: The mutual forces of action and reaction between two bodies are equal, opposite and collinear.)

    So this reaction is equal to e1 where the mass now is weight of gun, scope, sling, etc divided by g.

    Now that you have the physics, we can see that only things accelerating (F = ma) have an effect on recoil, not the case size.

    By the way, keep your velocity down, these equations go out the window as velocity of bullet approaches speed of light, something that really worries some scientists!
     
  5. J E Custom

    J E Custom Well-Known Member

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    There are two kinds of recoil, Recoil energy (Total force backwards) and Recoil velocity (The speed at which the weapon moves backwards ) This is sometimes called "Felt recoil".

    If you look at the formulas for calculating these types of recoil they do not include the case size
    or shape. Only the bullet weight,caliber, powder in grains,velocity and the weight of the
    weapon.

    Heaver bullets= More recoil, more velocity=more recoil, less weight of weapon= more recoil ,ETC.

    The only reason to feel a difference between two cartriges of different shapes if all other
    things are equal is the burn rate of the powder that is used. A faster burn rate that produces
    the same velocity with the same bullet and weight of rifle will reach peak pressure faster
    and increase recoil velocity and that might be mistaken for more recoil.

    It is as Dmci Stated (Newtons law applies).

    So even if it feels like it recoils more, if everything is the same it doesn't. Felt recoil can be
    deceiving because even the fit of the stock can change the perceived recoil. Just like if you
    hold a shotgun tight against your shoulder and fire it then hold it away from your shoulder and it will recoil more because in reality it weights less because you shoulder is not adding any weight
    to the shotgun like it does when held tight.

    I hope this helps explain your question.

    J E CUSTOM
     
  6. Loner

    Loner Well-Known Member

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    The bullets part of it, the gas is the other, muzzle brakes work for a reason.
     
  7. DMCI

    DMCI Well-Known Member

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    Another good question.

    Let's put this one in engineering terms. A firearm is really a machine that converts stored chemical potential energy (in the primer and to a greater extent the powder) into kinetic energy of the bullet in flight.

    Bottom line is we must look at the efficiency at which our one cylinder internal combustion engine operates. A whole host of variables are at play here. Bore, barrel length, bullet weight and configuration, desired muzzle velocity, etc.

    Compare for example the .45 Cal. Colt 1911 to .338 Winchester rifle. Different performance, different parameters, but both can shoot a 230 grain bullet. Comparing the .300 WSM to the .300 Win Mag is a much more subtle comparison but the same principles apply.
     
  8. Mikecr

    Mikecr Well-Known Member

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    Cartridge dimensions do affect recoil. Those that keep the burn nearest the chamber produce less recoil. These are highly bottlenecked cartridges like WSM/WSSMs.
    Those that combine and send a slug of unburned powder with the bullet produce higher recoil. These are more of the 30-06 proportions(a poorly designed case).

    And brakes? No they do not actually reduce recoil, because most of it has been set in motion by the time the bullet is released. Brakes are after the fact. Merely a last impression of the shot..
     
  9. Varminator 911

    Varminator 911 Well-Known Member

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    So you are saying short fat cases have less recoil, interesting. Does powder burn rate affect recoil? My thinking is faster burn rate might recoil more but that's not what you are saying.
     
  10. Varmint Hunter

    Varmint Hunter Well-Known Member

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    In theory; wouldn't an efficient case design (wsm, BR, etc) produce less recoil because it could generate the same velocity, with the same bullet weight, as a less efficient case that requires more powder to get the same job done?

    In short - Shouldn't the short/fat cartridges recoil less than long/thin cartridges when the other parameters are the same?
     
  11. J E Custom

    J E Custom Well-Known Member

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    In my opinion NO.

    The whole issue of a more or less efficient case has nothing to do with recoil it has to do with
    a more complete and consistant burn of a specific powder charge.

    Some think that the short fat cases burn less powder than the long slim cases do.
    in fact they can use more powder. A good example is the 7 WSM compared to the 7mm
    rem mag. I have both and the same velocity is reached with the same amount of powder.

    But when you up the pressure to the WSMs standard It takes more powder than the 7mm rem
    can/ should handel.

    My best load with the 7WSM and a 140 gr bullet is 71 grains and with the same bullet in the
    7mm rem it is 68 grains of the same powder. they both have a nearly identical velocity.

    The main purpose of the short fat cases is for a more consistant burn and lower SDs
    not recoil.

    In my earlier post I mentioned recoil velocity and burn rate effecting felt recoil .

    There are many things that can effect "Felt recoil" but the simple truth is that recoil energy
    remains the same if all conditions are the same.

    A poor fitting rifle will appear to have more recoil than a proper fitting one with all things being
    equal and if placed in a machine that measures recoil energy they will be the same.

    J E CUSTOM
     
  12. Mikecr

    Mikecr Well-Known Member

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    I don't know that anyone claimed short-fat cases come about -for less recoil, but they do produce less than some longer cases of the same capacity.

    If you look at a 30-06 it's fairly easy to see that there is almost nothing holding back the powder columb. This cartridge is an elongated funnel. So a good amount of powder mass combines with the bullet mass and this would need to be accounted for in accurate recoil calcs(it isn't). This bullet chasing powder burns slower as it's under less pressure when finally burned way down the bore. This increases muzzle pressure, producing a big ole fireball, ugly bullet release, and even more percieved recoil. Classic case in low efficiency..

    On the flipside, a very high efficiency cartridge/load burns completely, and at a consistent rate, before the bullet reaches the muzzle. The muzzle pressure is lower so it jumps less, and bullet release is cleaner.
    You will never see this with a long, skinny, high body taper, low shoulder angle case -for a given capacity.
    To do this means faster powder, or slower powder burned in or very near the chamber -as quickly as can be gotten away with. Highly bottle-necked cases contain powder better to make it burn right there.
    Examples of this were explored by Gibbs with front ignition, and I believe Vaughn validated it in 'Accuracy Facts'.

    We can follow this observing winning 1kyd IBS LG BR cartridges and see what settles into easiest to shoot(quickly) while producing satisfatory results. High recoil fire breathing cartridges won't do well here, and they fade from the lineup.
     
    Last edited: Nov 18, 2010
  13. Akmtnrunner

    Akmtnrunner Member

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    I know this is an old thread but I found it as I was google searching this topic. I was confused but now I've come to realise another way to think through it that may help others.

    I was having a hard time reconciling how the case dimensions do not affect recoil. As I thought through the entire recoil process, I could not get around how the pressure force is the force that causes the rifle to recoil backwards (besides the bullet-barrel forces, which are negligible and besides the point), yet the area that it acts upon to create force, is irrelevant?

    Until it occurred to me to consider portions of the case that pressure acts upon to create forward push like the taper and shoulder. As slight as their angles may be, the forward-area component will equal and cancel out the backward-area component that exceeds the caliber's area. In other words, as the case head increases size and does in fact receive more force acting rearward, the case's taper and shoulder must also increase in size and receive an equal amount of additional force acting forward. As long as the action is strong enough, nothing else feels any difference.

    Now I feel better :)
     
  14. Mikecr

    Mikecr Well-Known Member

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    Equal and opposite reaction. The force that propels a 200gr bullet to 2950fps, also pushes the rifle back at you. Add 20gr of unburned powder slug to that, and you now have 220gr accelerating 0 to 2950fps in front of your shoulder.
    A blank, any powder or pressure, produces little to no recoil, even while there is still energy to cycle gas operation. Recoil operation, won't work with blanks -because there is little to no recoil. There are muzzle jumps but not actual recoil.

    Bolt thrust itself is irrelevant to actual recoil. Pressure itself is irrelevant to actual recoil. Newton did not need to include these factors.