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A fact about choke tube shotgun barrels...

Discussion in 'Shooting Related Threads' started by Sportshot, Apr 24, 2010.

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  1. Sportshot

    Sportshot Active Member

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    I was looking at my Perazzi barrels today with The Unloader's barrel mic in hand and I was surprised at the large amount of overbore they machine at the base of the tube. The bore is running along at about .740, then, right at the base of the tube, the bore flairs open to about .755.

    I would have thought the point from bore to choke tube was flush or maybe a couple thousands at most. But to see that thing just expand out like that with about 12 or 15/thousands seems really odd.

    Does anybody remember the old Russian Tula Choke? That is actually what you have in a gun with choke tubes.
     
  2. Sportshot

    Sportshot Active Member

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    Is this typical of barrels with choke tubes?
     
  3. wireguy

    wireguy TS Member

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    There is an article where this is explained by The Technoid at shotgun report. Manufacturers make sure the bore is much narrower where it hits the choke tube so the rear of the choke tube is well shrouded lest it get blown out of the gun. The first part of the choke tube being much larger acts as a jug and actually causes the constriction in the choke tube to choke harder than it would without that flare out. The tubes should be designed to take that into consideration and marked correctly but..........................
     
  4. Unknown1

    Unknown1 Well-Known Member

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    I seriously doubt that the mismatch that usually exists is anywhere near great enough to qualify as a Russian choke.

    A number of tube manufacturers market their chokes as being "bore matched" and their ID at entry is closer to the diameter of the bore.

    MK
     
  5. pheasantmaster

    pheasantmaster Well-Known Member

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    Not all barrels are designed using the method you speak of.

    Not a Russian design or spinoff either.
     
  6. Paladin

    Paladin Well-Known Member

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    "large amount of overbore they machine at the base of the tube."

    It has a name, but I can't recall it. It's a common sense safety precaution, a safety relief for all of the various scenarios that can happen. Choke tubes that are moderately damaged/out of round in the leade area have been inadvertently installed. If the shot column snags the base or leade of the choke tube, permanent barrel damage usually occurs.

    I just mic'd my Kolar for length of overbore that seems to be the concern. The result was about .750 length of overbore in that area.

    The only 'Jug' choked barrel I measured had a full 2 inches of .010 overbore, with a tapered leade into the 'Jug' choke. The entire 'Jug' choking occurred just before the leade of the fixed choke.

    Does .750 have any affect, probably not much.
     
  7. Sportshot

    Sportshot Active Member

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    My Eyster barrel, which is supposed to be the most highly, technically engineered of the bunch is interesting. The barrel is backbored and I find that Ken machined .0009/1000's of bore constriction in the 1/2" preceeding the choke base. So the barrel bore tightens up,... and then BAM!, the mic gauge reads like it is falling off a cliff... the diameter blows out about .0018/1000's more from the newly tightened bore leading into the choke skirt, .... and then the choke tapers out to the normal .35/1000's full.

    No, - this is not a Tula choke obviously, but something very dynamic is going on n that last couple inches..... Genius, or mad scientict playing with his reaming tool?

    Briley is the same way though not as drastic.

    Were these guys building to some kind of imagined "safety standard" or is there a performance theory underling it all?
     
  8. Unknown1

    Unknown1 Well-Known Member

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    My bet is that it's just a gimmick to keep the competition guessing. There's only so much trick stuff you can do with a tube and I'm betting that it's been tried by more than one person a long time ago.

    If you want to want to see what I'm referring to, hang around with a bunch of fanatical card shooters some time. They've done things to shotgun barrels that most trap people haven't even imagined yet.

    MK
     
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