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How to read choke constrictions in tapered bore?

Discussion in 'Shooting Related Threads' started by Steve W, Nov 29, 2011.

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  1. Steve W

    Steve W Well-Known Member

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    I noticed couple barrels have similar bore worked like this:

    a) The bore at mid section is .738", then it tappers down to .735" two inches before the back of choke tube. What should I read the choke constrictions? Subtract from .738" or .735"?

    b) What if the tapper down starts only 1" from the back of choke tube? does it change the way measuring constriction?
     
  2. Calkidd

    Calkidd Well-Known Member

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    Given the fact the barrel has a restriction I would use the smallest number you found. After all the shot is entering the choke tube after traveling through the restricted barrel.

    Bryan
     
  3. BigM-Perazzi

    BigM-Perazzi Well-Known Member

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    I'd suggest using the bore diameter well clear of our chokes. Then subtract the minimum diameter from the choke.
     
  4. skeet_man

    skeet_man Well-Known Member

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    Think of the taper as a "pre-choke". So basically, add the taper and the choke, and subtract from the bore ID.

    When Remington built the Big Bore .745 1187 barrels, they had .018 of "taper" in the barrel before the choke, which acted as a pre-choke. They were shipped with "Trap Full", "Trap Extra Full", and "Trap Super Full" chokes. However, these were really Cylinder, Skeet, and IC. Because of the built in "pre-choke", the barrel ALREADY had .018 constriction into it, and the choke tube added to that.
     
  5. ccw1911

    ccw1911 Member

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    If most of the barrel is .738 and then tapers to .735 I would subtract the choke number from .738. If you had no choke tube in it you would effectively have .003 choke.
     
  6. TOOLMAKER 251

    TOOLMAKER 251 Active Member

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    Steve, I would say since you have several inches of .735 before it goes into the choke forcing cone that .735- choke diameter would be the choke constriction. Many years ago the US doubles gun Mfgs would use as much as 4" of transition in the choke area. I have seen several 32" SXS's with barrels cut down to 30" that still had some choke left in the barrels.
     
  7. slowdp

    slowdp TS Member

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    I would think you would subtract the smallest diameter from the larges diameter past the forcing cone. After all, you can have a barrel with parallel sides reamed to a larger diameter just before the exit and achieve a choke. Right?
     
  8. JerryP

    JerryP Active Member

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    THE UNLOADER told me the barrel diameter is at a point about 3" back from the choke tube. My barrel gets larger from that point to the choke tube.
     
  9. skeet_man

    skeet_man Well-Known Member

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    Jerry- What you are describing is in effect, a jug choke.
     
  10. daddiooo

    daddiooo TS Supporters TS Supporters

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    Have run across "jug" choked barrels several times but never understood why someone would have it done that way. What is the advantage of jug choking???
     
  11. short shucker

    short shucker TS Member

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    That fad of "jug choking" barrels ruined many a good gun the same way porting has.

    ss
     
  12. BigM-Perazzi

    BigM-Perazzi Well-Known Member

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    Really! ?? How so short.....
     
  13. miketmx

    miketmx Well-Known Member

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    There are 2 ways to measure a choke 1) constriction and 2) The resulting pattern percentage at 40 yards. I would be very curious about how these chokes actually pattern at 40 yards compared to conventional choke tubes.
     
  14. JerryP

    JerryP Active Member

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    skeet_man , It's a standard BT99 with factory choke tubes. I was wrong in my description, the bore gets larger in the last inch before the choke. Gary told me to back off about 3" from the choke and that would be my bore size. The bore is .736 all the way through until just before the choke, then it goes to .742. It is supposed to be .740 bore so I didn't know where the measurement should be taken.
     
  15. Rastoff

    Rastoff Active Member

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    miketmx is correct. The actual diameter of the choke is irrelevant. Measure your choke at the pattern board. Mark off 40 yards, shoot the pattern, draw a 30" circle and determine the percentage of pellets inside that 30" circle. This is the only real value.

    Rather than count the holes, take a digital pic and use this software to do the analysis for you: <a href=http://www.shotgun-insight.com/intro.html>Shotgun Insight</a>
     
  16. JerryP

    JerryP Active Member

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    Rastoff, That is fine but you still won't know the actual constriction until you measure it.
     
  17. Rastoff

    Rastoff Active Member

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    OK, so you measure the constriction and now you know that your choke has a constriction of .035". So what? What do you do with this information?

    The point I am trying to make is that it's the size of your pattern that matters.
     
  18. Two Dogs

    Two Dogs Well-Known Member

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    Bore and choke numbers are just figures that you tell your friends.....what really matters is what appears at 40 yds. on the pattern paper...
     
  19. daddiooo

    daddiooo TS Supporters TS Supporters

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    The question persists....what is/was the purpose/advantage of jug choking a barrel??
     
  20. chipking

    chipking TS Member

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    Jug choking remains the only way to get anything other than cylinder patterns from a straight cylinder bored barrel (as in muzzle-loader) consistently. Anything in excess of the length of the shot column immediately before the actual choke becomes the final "bore" that the shot sees before entering the choke constriction so for constriction number purposes a straight .735 bore to a .700 choke would have 35 thousandths constriction and the same barrel with a 2" long .745 section (jug)just before the choke would have 45 thousandths constriction. AND the .735 straight bore with the .745 jug now has 10 thousandths constriction. Not a lot but when people were used to nothing for many years that little bit of improvement probably seemed like MAGIC and gave the JUG Choke a place in shotgun legends forever.

    How either would pattern depends on a bunch of other items (bore quality, choke quality and design) as well as just the pure constriction amount.

    If you think about it most of your choke tubes are a jug choke to some degree. They must be larger than the bore to prevent snagging and if they have a long lead that is larger than the bore then tapers to the final choke you have a classic jug.

    --- Chip King ---
     
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