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Cones, Bores, and Chokes - #2

Discussion in 'Uncategorized Threads' started by BDodd, Apr 18, 2007.

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  1. BDodd

    BDodd TS Member

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    Here's the second section on the Tom Roster article in Sporting Clays Magazine. Remember, these are regarding his work and not mine:

    Over-Bored Barrels......
    "Over-boring, or back boring, is currently also a popular fad in shotgunning. It's hard to buy many specialized models of target shotguns and even turkey or waterfowl guns that do not feature over-bored barrels.


    "The burning question is, 'Does over-boring really do anything, and, if so, what should the dimension be?' To find out, I had 12-ga barrels over-bored in .005" increments from a starting dimension of .730", then measured the effects on patterns and velocity.


    "I found that out to a finished dimension of no greater than .745" (.015 increase), I measured improvedment in pattern density by as much as 10 - 15% at 50 yards with lead shot loads, especially in shot No. 5 and larger. For shot sizes 6 through 8, I commonly measured an improvement of about 7% in pattern density at 40 yards. With steel shot loads in all shot sizes tested (6s through BBs), I measured an across-the-board increase in pattern density of about 5% at 50 yards and as much as 10% at 60 yards. In sum, there is a small (but to some shooters important) improvement in pattern density as a result of over-boring 12-ga barrels no larger than .015 from standard.


    "Over-bores greater than .745" in 12 gauge were found to also produce improvement in patterns with both lead and steel shot types. However, and this is a big however, after .745", I started to measure increasing velocity loss for both the lead and steel loads tested in such 'radically' back-bored barrels. The velocity loss was greatest with the steel shot loads, due, no doubt, to the lessened ability of the typical stiff steel shot wad's obturating skirt to expand large enough to seal the bore properly (contain powder gasses) as the over-bore exceeded .745".


    The Lesson? Back-boring is good for pattern performance up to a point but then becomes a negative, especially in terms of velocity loss. My findings indicate that a 12-ga. barrel over-bored to a finished diameter larger than .745" is a minus, if not a downright mistake, and .740 is better yet."
     
  2. miketmx

    miketmx Well-Known Member

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    I wonder if he mentioned anything about constriction, like was the constriction the same before and after the backbore??
     
  3. zzt

    zzt Well-Known Member

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    Thanks Bob. BTW, hope you are healing well.
     
  4. BDodd

    BDodd TS Member

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    zzt - thanks, so far so good - hope to shoot sometime in May. Constrictions, Mike? There was no mention of whether or not the chokes were changed at this point (but highly doubted) however, chokes will be covered in tomorrow's episode. All these writings are complete, nothing left out that was pertinent but I did leave out some preliminary fluff from the first offering....breakemall....Bob Dodd
     
  5. Harold

    Harold TS Member

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    I think what Mike was getting at is that backboring the barrel while leaving the choke the same diameter results in a tighter choke expressed as the difference between the bore and choke diameter. So what was kept constant, the choke diameter or the constriction? If the former, you would expect a tighter pattern to result, and this would not really be an "improvement."
     
  6. Neil Winston

    Neil Winston Well-Known Member

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    Thanks for posting this, Bob, and I too wish you a speedy recovery.

    Maybe I'm biased, but for my money TR's article doesn't hold a candle to the many patterning threads I've posted here and which can be searched for under with the keyword "Winston".

    I don't want descriptions of the data, I want the data themselves. If patterns increased 7% don't just tell us, show us the ten "before" patterns and the ten "afters." It's easy; I've done it here dozens of times.

    My second reservation is that I've never gotten such data. Everything I've tested showed _no_, I repeat, _no_ increase in pattern density attributable to bore diameter. He may have gotten it, and the way he did the experiment if fine. But time after time I've compared stock Perazzi (and now a single 870 barrel) barrels to various overbores and the only top-performing overbore is a Bowen and it has 0.040 choke and that's what you expect to be tight, isn't it?

    His data with larger shot sizes may well be exactly right. As may his chronograph data.

    Neil
     
  7. joe kuhn

    joe kuhn Furry Lives Matter TS Supporters

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    Good distinction there Harold. Wonder what the author would say.
     
  8. BDodd

    BDodd TS Member

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    Mike and Harold, I'm with you on this consideration. Tomorrow's episode on "chokes" will include how to reach Tom via E-mail or snail. It'd be fun to see any response. Neil, I'm also kinda Missouri-born on these flat statements and that's why my certainty that the opinions are those of Mr. Roster and not necessarily mine. However, I thought it would be good for those that blindly assume all these gadget fixes can be misleading, less than stated, and having results somewhere else than where it was intended....Bob Dodd
     
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