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Choke Constriction: Tech Question

Discussion in 'Shooting Related Threads' started by Chango2, Jan 27, 2012.

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  1. Chango2

    Chango2 Active Member

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    Was discussing choke constrictions with a friend tonight. He is well-versed re. trapguns and he mentioned, and I will try to be precise:

    "Barrels that have a bore larger than nominal, that is bigger than .729, the standard for a 12 gauge, in general, say .740 to .750, which are now becomming more like a contemporary standard, require less "choke" to throw a tighter pattern."

    In other words, say "20 points" of choke will throw a tighter pattern in a .740 barrel than it would in a .730 diameter barrel. I am not talking about choke diameter per se in actual numbers, but in relative degrees of difference (in thousandths) between bore diameter and choke diameter.

    In other words, a bigger bore requires less choke to throw a tighter pattern compared to a standard .729 inch 12 gauge bore?

    Is this "clubhouse/urban myth", information put out by mfg's., actually seen and documented either via anybody taking the time to pattern a gun(s), or hard evidence put out by the firearm or ammunition industry?

    ....Inquiring minds, I'm compulsive enough to wonder because I've not seen this either supported or discounted in any "official" literature from shotgun or ammunition or barrel maker..

    Thanks,

    David
     
  2. wayneo

    wayneo Active Member

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    IMO, I would have to say yes they do throw a tighter pattern, and a more consistent pattern. I have a higher pellet percentage in a 30" circle at 35 yards with an Invector+ Full tube than I ever had with an Ivector Full or just a Full choked Browning barrel.

    So I'm thinking with a higher percentage pellet count with a back-bored Invector+ barrel, I would need more constriction with the other barrels to match that, no?

    Wayne
     
  3. cubancigar2000

    cubancigar2000 Well-Known Member

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    Thats why they make Big Bores, your friend is right on the money. How ya been David?
     
  4. hmb

    hmb Well-Known Member

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    The theory is that big bore barrels perform better than standard bore barrels. This is the result of less shot deformation resulting in fewer pattern fliers.

    One of the early big bore barrels had a tapered bore, that particular barrel used chokes with less constriction. HMB
     
  5. Setterman

    Setterman Well-Known Member

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    Depends on the gun.
     
  6. Unknown1

    Unknown1 Well-Known Member

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    Dr A C Jones differs with the OPINION that big bores produce better anything (Sporting Shotgun Performance, Ch. 20, "Effect of Bore Size on Patterns").

    He indicates that the manufacturers that sell them have yet to provide any definitive proof of the advantage of oversize bores. He also notes that Perrazi has a line of "Pro-Sport" guns that have bores that are actually a bit smaller than standard. He offers the further opinion that this may be the proper direction given some of the disadvantages of large bores.

    Keller
     
  7. halfmile

    halfmile Well-Known Member

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    Take any 2 guns, right next to each other in the production line, same dimensions in all respects, and the damn things will still not perform the same.

    They're kind of like women but they don't talk back. They WILL spend your money, though.

    HM
     
  8. Johnny

    Johnny Well-Known Member

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    hmb, the problem with the "theory" is that it's all blow and no show.
     
  9. racer

    racer TS Member

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    No proof of better patterns from a larger bore. Marketing at it's best. Sell stuff that folks think is better with no way to prove otherwise! Dan
     
  10. HSLDS

    HSLDS Well-Known Member

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    Another aspect is the constriction relative to WHAT bore diameter???

    If I start with a 0.730 bore and give it 0.010 constriction - I get an effective exit hole of 0.720 - approaching improved cylinder.

    Put that improved cylinder choke into a 0.750 bore and I still have an exit hole of 0.720 - or a 0.030 constriction - right on the edge of improved modified - full.

    Try a 0.740 barrel and you end up with 0.020 constriction - or a modified choke.

    Many choke tubes will fit in guns with varying bore dameters.

    How many of you know the true diameter of your bores???

    Seminole advertises tubes specifically addressing this issue - they want to know the true bore diameter of the barrel and then will provide tubes giving constriction relative to that diameter. There are others who will make them too, but it is not the forefront of choke selection in the USA.

    Food for thought.
     
  11. Chango2

    Chango2 Active Member

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    HSLDS: That's not what I meant. Perhaps this is a hard question to phrase. What I mean is simply, to give an example: If a .740 bore "runs" with a choke of .720 bore, giving it 20/1000 inch of contriction, will its patterns be tighter, all else bieng equal, than say a .730 bore "running" with a choke of .710 bore giving it also 20/1000 inch of constriction. Will, all else being equal (forcing cone dimension, choke design, ammunition) the patterns be the same or will the patterns of the .740 bore and the 20/1000 inches of choke restriction be either more even or denser?

    Again, I don't know, but have been told that this is roughly the case,but I don't know where that is "in the literature" or who or what company has demonstrated any differences in an objective and controlled testing situation. I suspect that bigger bores than .729, up to a *point, will give better patterns with less net choke restriction for a variety of subtle and not so subtle reasons, but generally because the shot is "handled" in a more gentle fashion...but I bet that's not the only reason. It is what I subjectively "see" at the range, but I don't know if this is true in EVERY case, but I sure suspect it given performance of Invector Plus barrels, a Kolar I observed (.740 bore) that just obliterates targets with 16/1000 inches of choke restriction and indifferent promo ammmo at the 16 yard line, etc. I suspect this is the case and have faith in many who state this, but wonder where it is reported objectively after unbiased ("scientific") investigation and testing.

    Determining bore internal diameter and choke internal diameter is easy with an internal bore mic...they are sold rather inexpensively by various individuals and companies and accurate measurements to 1/1000 of an inch or better are easy to obtain.

    Guns I have shot with "overbored/backbored" barrels, (terms refer to almost the same thing) generally shoot with less felt recoil.

    Again...it's inquiring minds...

    Thanks,


    David

    *point being where gases escape around the wad or cold weather gives a hugely overbored barrel to overtax the sealing of a wad...e.g. abore of .775 and more...there have been some "special ones made" over the years....see Baker Barrels..
     
  12. 4th. down

    4th. down Active Member

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    Just the opposite. If you had the same choke constriction in a .740 bore vs. nominal .729 bore, you get more open patterns and better distribution. If you would want a modified performance out of a nominal bore 12 ga., then you would need to go to an Imp. Mod. in a .740 bore to get as tight a pattern.

    I went thru all of this with Kerry Allor and all else being equal, same load, shot the same day under the same conditions, etc., this is what would happen as stated above.
     
  13. Unknown1

    Unknown1 Well-Known Member

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    <blockquote><I>"Guns I have shot with "overbored/backbored" barrels, (terms refer to almost the same thing) generally shoot with less felt recoil."</I></blockquote>Oh, PLEEEZE... another one with a micro-calibrated shoulder.

    It couldn't be that those over-bored guns were balanced differently or fit you differently/better? Or maybe your pre-washed brained just EXPECTED to feel less recoil?

    Keller
     
  14. sabretooth

    sabretooth Member

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    The best explanation is in Bob Brister's book" Shotgunning. The Art and the Science".
    Main effect of wider bore diameter is shorter shot column height for same number of pellets. As the pellets start to accelerate due to rising gas pressure, pellets at the bottom of the shot column push against the ones on top which move very slightly later. They become deformed /faceted & fly off the true path they would have taken had they remained perfectly spherical. Hence the loss of pattern density.
    Overboring reduces overall shot column height & percentage of pellets that would be deformed.

    Another method described was to put Grex ( inert ) powder between pellets to prevent them from deforming. If one shot that kind of ammo same constriction would behave like a tighter choke.

    Same effect is achieved by Copper palted pellets or adding Antimony to lead...pellets are harder & less prone to deforming under pressure.

    Type of choke is technically a different matter. Relative constriction is one factor. The other factor is type of choke... Jug choke, simple swage choke, tapered choke etc.
    One of the best books I ever read on the topic.
     
  15. BD457

    BD457 Member

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    seems to me that the major arguement for/against any theory is the deformation of pellets. Has there been any tests using steel pellets? Eliminate the deformation variable in the test procedure. I'de be very interested in the results.

    Mike
     
  16. Chango2

    Chango2 Active Member

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    BD457: Using steel shot to compare bore-choke-pattern variables sounds like a great investigation!
     
  17. millerm12

    millerm12 Member

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    for sure the bigger the bore the less restriction you will have to use.my brother always shot a 780 bore with his beretta and used 15 thousands choke and would still roll smoke off of a 27yard target.not to mention you gain approximately 150 to 200 fps on your shell.the only down fall to the big bore i could see was that your shot pattern was shortened slightly due to the larger denser pattern it produces.but recoil was reduced to almost nothing.also you have to shoot a shell or wad that has a deep powder cup or sometimes the shell sounds hollow or light because of wad not sealing up in the larger barrel.never had that problem with a 740 bore but a 780 bore you need to pay attention to shell selection or type of wad to reload.
     
  18. brownk80

    brownk80 Member

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    HEY, we talking 71/2's or 8's here?
     
  19. millerm12

    millerm12 Member

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    7 1/2 1 1/8 loads
     
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