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Bore size, velocity, ejecta weight and recoil

Discussion in 'Shooting Related Threads' started by School Teacher, May 9, 2011.

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  1. School Teacher

    School Teacher Well-Known Member

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    I there a relationship between bore size, ejecta weight, velocity and recoil?

    Does a 1 oz. load from a 20 gauge at 1200 fps have less recoil than a 1 oz. load from a 12 gauge at 1200 fps assuming identical gun weight?

    I remember reading somewhere that one reason the .270 had less recoil than a 30-06, shooting the same weight of bullet at the same velocity was that the .270 had a smaller bore size.

    Ed Ward
     
  2. scott calhoun

    scott calhoun Well-Known Member

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    There is a formula for calculating recoil. Bore size is not part of it. Ejecta weight, velocity, recoil and gun weight are the components. Hodgdon used to publish it in their reloading manual. I suspect a google search would find it pretty quickly.
     
  3. timb99

    timb99 Well-Known Member

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    The answer is, sort of, but its not a direct relationship.

    Assuming the guns weigh the same:

    A .270 will recoil slightly less because there is less ejecta weight (assuming same bullet weight and muzzle velocity) because the .270, comparing powder for powder, takes less powder to get a bullet to the same muzzle velocity as a .30-06' takes.

    I checked Hodgdon's tables for a 150 grain bullet using IMR 4350 and a 180 grain bullet using H4831. Both sets of data had those bullet weights and those powders.

    In both cases, the .270 got to the same muzzle velocity with less powder.

    The weight of the powder, when it comes to high powered rifles, DOES make a difference in recoil.

    Now, part of the answer is, "why does it take less powder for a .270 to get the same weight bullet going as fast?" The answer to that is because of the smaller bore size and therefore less volume.

    You can see the same thing if you compare a .308 Winchester and a .300 Win-Mag. Case volume affects how much powder it takes to get the same weight bullet going the same muzzle velocity, and therefore the .300 Win-Mag will have more recoil due to the greater mass of the powder (again, assuming the gun weighs the same.)

    For a 20 gauge, its hard to compare directly, because so few powders are common from 20 gauge to 12 gauge, but assuming both guns weigh the same, and if you could use the same powder, I think the answer is, which one requires more powder for the same weight of shot/wad and the same muzzle velocity? (I'd guess the 12 gauge takes more powder due to larger volume of the case/barrel.) Then, of course, you have to ask, can you tell the difference, because about 95% of the recoil of a shotgun is due to the weight of the wad and the shot, and only a small fraction can be attributed to the powder.

    So it may not even be, to use Neil's wording, a "just noticeable difference."

    Now, keep in mind, this all assumes the data tables are accurate. and we know, sometimes they're not.

    Your mileage may vary.
     
  4. mike campbell

    mike campbell Active Member

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    "Does a 1 oz. load from a 20 gauge at 1200 fps have less recoil than a 1 oz. load from a 12 gauge at 1200 fps assuming identical gun weight?"

    No.
     
  5. spitter

    spitter Well-Known Member TS Supporters

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    What about differences in weights of the wad and powder used in 12/20 gauge... small maybe, but accountable in the formula...

    Jay
     
  6. timb99

    timb99 Well-Known Member

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    MK

    Maybe I wasn't clear.

    For the same bullet weight at the same muzzle velocity, the .270 will have less recoil because it requires less powder.

    Powder is part of the formula.
     
  7. sliverbulletexpress

    sliverbulletexpress TS Member

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    Does expanding gas have weight?
     
  8. timb99

    timb99 Well-Known Member

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    silverbullet

    Absolutely, positively. The mass of the powder doesn't disappear, it just undergoes a chemical reaction, but the mass (or weight, if you will) remains the same.

    Its part of the recoil formula, but it is treated a little differently than the bullet.

    And when it comes to high powered rifles, the effect of expanding gases can make up a pretty large percentage of the overall recoil.

    This is precisely why muzzle brakes actually work to substantially reduce recoil in high powered rifles.
     
  9. skeezix

    skeezix Member

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    Usually the 20 gauge has more recoil - because 20 gauge guns tend to be lighter. The 20 gauge may use a bit less powder and a slightly lighter wad - both of which decreases the mass of the ejecta and results in lower recoil energy - but the weight of the gun will be more significant.

    The same recoil energy calculation applies to the '06 and the .270. If the .270 has less recoil it's because it has a lower powder charge ( I didn't look up any loads - I don't know if a typical 150 gr. load for a .270 uses less powder than a typical 150 gr. '06 load or not)

    john
     
  10. spitter

    spitter Well-Known Member TS Supporters

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    Powder Weight and Ejecta Weight are two separate variables under the formula...

    Jay
     
  11. skeezix

    skeezix Member

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    yes it is, powder is part of the ejecta - but the formula assigns a value for the velocity to use for the powder that is different than muzzle velocity.

    john
     
  12. Limpy100

    Limpy100 Member

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    Scot bore size does make a differnce. If you put 18 gr of powder in a 12ga and 18gr of powder in a 10ga pushing the same load the 10ga cant build the same pressure because of more volume to fill.
     
  13. scott calhoun

    scott calhoun Well-Known Member

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    I reviewed a few recoil calculators that I could find on the internet (Google is your friend) and none of them contained any reference to bore size. I should add that I'm not trained in math or physics and have no professional education or certifications that would allow me to verify that these calculators/calculations are correct. However, in all calculators that I searched they all used the same input variables - and bore size was not one of them.

    Further to Limpy's point, there is no reference to pressure in any of the calculations either.
     
  14. 870

    870 Well-Known Member

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    I guess Neil has really gone cold-turkey.
     
  15. Limpy100

    Limpy100 Member

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    Put 10 grains of powder in a 32 and the same in a 357 and same load ball and check the velosity.
     
  16. scott calhoun

    scott calhoun Well-Known Member

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    Limpy -

    I think to clarify the reason why bore size and pressure is not part of the formula is that those variables affect velocity. Velocity is part of the formula, so as long as you have the velocity, bore size and pressure are implicitly included. Same load in two different bore sizes will result in different velocity, thus different recoil.

    Then again, I went to public school . . .

    Scott
     
  17. Hap MecTweaks

    Hap MecTweaks Well-Known Member

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    "A .270 will recoil slightly less because there is less ejecta weight (assuming same bullet weight and muzzle velocity) because the .270, comparing powder for powder, takes less powder to get a bullet to the same muzzle velocity as a .30-06' takes."

    Where does that leave the heavier gun theory as kicking less or having less felt recoil?

    Years ago my buddy had a Ruger .270 and I had the Ruger 30-06, both weighed within an ounce or two being the same weight. We were working up loads for an elk hunting trip to CO. We began with Doug trying 150 grain Noslers in his .270, I already had my load developed, a 180 grain Nosler. We tried both rifles with 150 grain bullets and Dougs .270 seemed to have a more rapid sharp recoil than my 06 did? With both of us shooting each others rifles, both of us had that same perception! According to the theory a heavier gun has less felt recoil holds true in this instance. I believe there's other things in play also, like the OAL of the bullets and drag on them getting to the same velocities.

    How does weight of ejecta apply to a compressed air gun? Those also have recoil too! I have a hard time buying the weight of the powders or propellant being a part of that equation. If the weight of the projectile and velocity is the same, the recoil is also the same but feels different in the process of how the velocity is attained.

    What about an .800 bore shotgun and one with a .724 bore and both weigh the same? Both at 1145 with the same payload, is there a real difference in recoil or merely a difference in (felt) recoil?

    Hap
     
  18. scott calhoun

    scott calhoun Well-Known Member

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    Hap -

    You are talking about felt recoil (seemed to have a more rapid sharp recoil than my 06 did). Felt recoil is another thing completely from actual recoil.

    The ejecta weight of powders are part of the equation, but if you play around with the calculator you'll see they are a much smaller part (because they make up a small percentage of the overall ejecta).

    As for the difference in bore sizes - if the velocity is impacted by the bore size then so will the calculated recoil.

    Scott
     
  19. Hap MecTweaks

    Hap MecTweaks Well-Known Member

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    Scott, what about the smaller caliber gun also having less felt recoil which has less powder weight? Recoil is recoil regardless of how the velocity is attained. True, felt recoil is different than actual recoil. A 100 pound shotgun would have the same recoil forces as a 5 pound gun would but it would certainly feel different. I think the bulk of misunderstanding recoil from felt recoil lies in fit and weight of the guns.

    The force necessary to push a .270 150 grain long bullet through the bore is far different than that necessary to push an 06 150 grain short bullet through at the same velocity.

    Hap
     
  20. scott calhoun

    scott calhoun Well-Known Member

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    Hap -

    A 100 pound shotgun would have the same recoil forces as a 5 pound gun? Not according to the formula at least. A 1.125 ounce load at 1200 fps in a 5 pound gun will result in 28.98 ft/lbs of force. That same load in a 100 pound gun will result in 1.44 ft/lbs of force.

    And I'd argue (but not very hard because I'm getting tired of the entire subject) that you could alter the felt recoil of either one depending on how the gun was setup (standard stock, custom stock, PFS, etc.).

    Scott
     
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