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Bore Diameters - Interesting Results!

Discussion in 'Shooting Related Threads' started by timb99, May 28, 2010.

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  1. timb99

    timb99 Well-Known Member

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    Just to satisfy my own curiosity, and also because I'm an engineer geek, I borrowed a friend's bore gauge just to see what the bores on my various guns measure.

    I was surprised at a few of the results.

    Zoli Skeet O/U - 0.726" top / 0.726" bottom<br>
    Zoli Trap O/U - 0.7245" top / 0.724" bottom<br>
    Stoeger Condor O/U - 0.729" top / 0.730" bottom (yeah, I know its a cheap gun, but its served me well)<br>
    CZ 712 Semi Auto - 0.724"<br>
    Remington 1100 30" magnum I just bought - 0.735" (kind of a surprise it was that big, plus its choked 0.697" for a 0.038" constriction.)<br>
    Mossberg 500 - 0.732"<br>
    Mossberg 18.5" barrel - 0.731"

    Now here's the one I was most surprised about:

    My daughter's left-hand 1100 step-rib trap barrel - 0.745" Cripes, no wonder she vaporizes targets with a 0.705" improved modified choke tube.
     
  2. Bob Hawkes

    Bob Hawkes Well-Known Member

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    timb99, You don't need to be an engineer geek to be interested in the real choke designations. One of the best tools to own is a bore guage, then you know what you really have in the barrel. Both intereting and educational. Check out Garry's guage, handy to have. Shoot often while we can, Bob
     
  3. ABH

    ABH Member

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    Timb99,


    With a 745 bore and 705 tube, your daughter is shooting a .040 choke barrel.Thats Full or Xtra full in anybodys book.

    ART H.
     
  4. pheasantsgalore

    pheasantsgalore Active Member

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    Remington ALWAYS had a great "thing" going with their 1100. Even their 870's in trap version, were larger bore. I believe, this is why the 1100 is still a great choice, period !!!!!!!!
    Rob G.
     
  5. shrek

    shrek Active Member

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    If you measure enough barrels you will soon find there is a lot of variability out there.

    For instance I have measured Remington 870 barrel bores, not the choke part, that have measured anywhere from .720 to .740, these were all fixed choke barrels that were not the ones that are supposed to be overbored.

    I like the ones that measure at least .732 and up.
     
  6. cubancigar2000

    cubancigar2000 Well-Known Member

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    I own a Gary Bulley Bore Mic and don;t know why I did not buy one a long time ago. I really find it helpful in knowing my exact choke constriction and it has been quite interesting to say the least.
     
  7. PerazziBigBore

    PerazziBigBore TS Member

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    Numbers are a wonderful thing.. but mean nothing when it comes to bore/choke relationship.. It's only a starting point.. I have a great barrel O/U .738 bore top and bottom.. .028 bottom.. .038 top On paper 2% difference at 30 yards.. Both barrels destroy targets.. but I'd have thought a .010 difference in choke would be more than 2%..
     
  8. Steve W

    Steve W Well-Known Member

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    Mike you're certainly right. They're only numbers on the dial. How it comes out the tube can surprise you.

    How many of you have two or more bore gauges? The two I have read differently on the same barrel, once I figure out the steady difference from many tests, I stay with the one read close to the barrel markings.

    The setting ring can be slightly off too, 0.002" difference in certain part of the ring can throw you off.

    BTW, reading can be way off in the chokes if you didn't clean it right. I use cheap soft steel knives to "peel" off any deposits.
     
  9. Rastoff

    Rastoff Active Member

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    Y'all need to be careful when using these gauges. ALL of the dial gauges at best have an accuracy of +/-.001" or +/-1 division. So, reporting a bore diameter with four digits of resolution is wishful thinking. Further, they have a lot of backlash which just compounds the measurement errors. The gauges I've seen are OK to get a general idea of what the bore is, but not really precise. They are a good tool to measure the DIFFERENCE between bore and choke if you use them properly. If you wiggle them back and forth a lot, then the backlash becomes a problem.

    Plus, none of this matters. Go to a pattern board and look at your pattern. Once you see the pattern based on size vs distance shot, who cares what the barrel and choke measurements are?
     
  10. timb99

    timb99 Well-Known Member

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    Guys. I agree absolutely. I just thought it would be interesting to know. And it is.

    Plus, it just goes to show you that the standard 0.729" bore diameter is not so standard.

    They're just numbers.
     
  11. maclellan1911

    maclellan1911 TS Member

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    I think the only thing standard about .729 dia. is.......Well how small is to small below that standard.
     
  12. Sky Buster

    Sky Buster Sky Buster TS Supporters

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    I just purchased a new Browning XT Unsingle. The modified choke
    measures .018 constriction. The improved modified measures .019
    I would'nt have known the discrepency without a bore gauge. I
    sent the Im. Mod. back for replacement.
     
  13. Sportshot

    Sportshot Active Member

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    I've had a lot of fun with mine, way more than $100 worth. The most interesting discovery to me has been with my various choke tubed guns. The measurement variations that occur between the bore and the point of contact for the skirt of the tube will drop your jaw.

    I would have thought, for example, that a nicely fitted choke tube would be less that a few thousandth's between bore and tube. I found it is common to have 10 to 15 thousandths. In fact, that is apparently a Ken Eyster "specialty" of blowing out the tube base and tapering a nice slow constriction. Just my observation on one of his barrels that I happen to own.

    I also know this, for whatever it means..... the Briley thin walls are the ones that have the tightest tolerances between bore and tube, dropping off less than one or two thousandths.... Perazzi tubes also blow way out and then tighten back up...

    Best barrel (I own) is a Wilkinson 34" .737 bore with .033 of fixed constriction. Very finely machined.
     
  14. OldGoat

    OldGoat Well-Known Member

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    A thought: A man with one watch knows what time it is; a man with two is never sure.

    A question: Who is the supplier which I have seen on TS.com who offers good bore gages for a very reasonable price? Thanks, Ed
     
  15. shrek

    shrek Active Member

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    The person with the bore gauges goes by the user name unloader on this forum.
     
  16. OldGoat

    OldGoat Well-Known Member

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    Shrek, Thank you very much for the info! Need to order one. Best Regards, Ed
     
  17. John Lloyd

    John Lloyd TS Member

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    How does one get in touch with Gary Bulley to buy a bore mic? Phone #? web site? Thanks JDL
     
  18. Steve W

    Steve W Well-Known Member

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    You may compare the one from Brownells as well.

    I have not seen two gauges read exactly the same from the same barrel, some could be off by 0.004" from another.
     
  19. Bob Hawkes

    Bob Hawkes Well-Known Member

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    That may be true Steve, my 2 are within .002 of each other, but they'll give you the right relationship bore to choke or barrel to choke tube. Then you need to decide which ones are giving you good breaks or patterns. The handiest part is sorting out mis-marked tubes and barrels. Shoot often while we can, Bob
     
  20. sernv99

    sernv99 Active Member

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    what's a good bore mic brand to buy?
     
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