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Bore Diameter Problem - - GunDr or Somebody

Discussion in 'Shooting Related Threads' started by cementman, Feb 1, 2010.

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  1. cementman

    cementman Member

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    Just recently purchased a 12 guage Beretta 471 Silverhawk SXS shotgun. Gun was used but in mint condition and seems to fit me very well. With the cold weather have not had a chance to pattern the gun but looking forward to this along with busting some clays.

    In the meantime have had the chance to use my bore micrometer and see what the constrictions are, bore and the Optima choke diameters. Whoa, a big flag came up with the results and wonder what concerns might I have.

    Bore diameter was particular on the tight side - - - - .724

    Optima Chokes were: Cylinder .732
    Skeet .729
    Imp Cyl .724
    Modified .718
    Imp Mod .705
    Full .693

    As you can see the variance between the differant chokes fall in line where they should be but with the bore diameter at .724 I see the Imp Cyl being a "Cylinder" choke.

    Please, anyone give me some direction on my problem here.
     
  2. timb99

    timb99 Well-Known Member

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    Its not a problem.

    My Zoli, and many Perazzi guns (and apparently your silverhawk) have slightly smaller bore diameters. My barrels are stamped 18.4, which is 18.4 mm. Yours may also have this marking.

    Yes, the standard choke tube constrictions are a little different. It may require you going out and patterning your gun to make sure you are comfortable with what kind of pattern each choke throws.

    You might just have to remember to use a full choke tube when you want an IM pattern, and a improved modified choke tube when you want a modified pattern.
     
  3. hmb

    hmb Well-Known Member

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    Is the bore of that shotgun tapered? If it is .724 from begining to end then something is wrong. Your skeet choke for example has no constriction. Normally a skeet choke has .005 constriction, that would mean it should be .719. HMB
     
  4. TOOLMAKER 251

    TOOLMAKER 251 Active Member

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    The older Beretta's like the 680's came through with bore diameters around .719 are you sure you have the right choke tubes? were they called Beretta mobile choke back then?
     
  5. alfermann66

    alfermann66 Member

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    Do you have the correct tubes for the gun? Did you measure the tubes all the way through, because they're bigger at the breach end than the muzzle?

    Buz
     
  6. Neil Winston

    Neil Winston Well-Known Member

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    An Optima bore should be more like 0.732 I think.

    There should be numbers starting with "18." stamped on it. What are they?

    Neil
     
  7. TOOLMAKER 251

    TOOLMAKER 251 Active Member

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    Beretta has been making the Silverhawk since the 60's but your 471 is a new production. I think you better recheck your sizes again.
     
  8. cementman

    cementman Member

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    Yes, measurements have been checked and rechecked numerous times. Yes, the chokes "Optima" are the correct ones for the Silverhawk 471 Beretta. The barrel reads .724 continous until reaching the choke tube then jumps up to .750 before entering the choke then at the end will steady out at the choke configuration. My dilema is that the .724 bore corresponds to a measured Improved Cylinder choke of .724 which would be a actual cylinder bore. Based on this what would be the results of the Cyl-.732 and Sk-.729 - - - maybe, super cylinder choke????
     
  9. Mapper

    Mapper Member

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    Sounds like you may want to spend some time at the pattern board. That .750 sounds like it is jug choked. If so, the chokes may work as marked.
     
  10. Bob Hawkes

    Bob Hawkes Well-Known Member

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    Cementman, This is from a cementhead. What you have found is the same as I have on a couple of different guns/choke tubes. Now you know the benefit of having a bore guage. I have assumed and found as you are, you're shooting cylinder until you get into a tube tighter than your bore size. Shoot well and have fun, Bob
     
  11. cementman

    cementman Member

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    In regard to barrel markings, checked the Beretta 471 along with a couple of other Beretta 391 barrels with the following markings:

    Beretta 471 ??Optima Bore?? Bore: .724 Barrel Marked: 18.4
    Beretta 391 Mobilechoke Bore: .723 Barrel Marked: 18.3
    Beretta 391 Optima Bore Bore: .733 Barrel Marked: 18.6

    Prior question was what is the barrel marking, what do the markings represent?
     
  12. GunDr

    GunDr Well-Known Member

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    I remember some time ago, a manufacturer that I cannot remember, had choke tubes just as you decribed. It seemed at the time that the chokes all measured approx .005-.010"" more than what they really should have been. Matbe it was Beretta.

    The cyl choke was .005" larger than the bore, skeet matched the bore, and so on.

    I would give Beretta a call and run this past them. If they can help you out, you can either remember want the true constrictions are or, polish off the choke designation and remark them, along with adding another notch on the end of the choke.

    When Browing first came out with their invector system, their chokes also ran a little over-sized.

    For a lot "hunters", they think there are only 3 chokes available on most guns, ic, mod, full. With this logic, an ic can be .005"-.020", mod can be .020"-.030", and full can be .030"-.045". Target shooters tend to be a little more picky in their choices.

    Doug
     
  13. Sam Ogle

    Sam Ogle Member

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    I offer the complete solution:

    Whatever you do........DO NOT pattern the gun.
    Patterning is a waste of shells and paper, and besides, who cares? Beretta is new at this gun-making game, and probably has a lot of idiots working there.
    Instead, write down the figures you have provided on this site, and feverishly re-calculate them each evening, just before going to bed, then upon arising in the morning, re-check them just in case there is an error. Or, something you forgot, or there is more wind outside today. Perhaps buy a newer, more expensive micrometer as well.

    As a matter of fact; simply send me the actual gun and the chokes, because who really cares how it actually patterns. That is inane, silly, and the mark of someone who is totally anal in their thinking.
    In the spring, I will walk up to a pattern board, mark a point of aim, walk back a measured distance,then execute the completely silly act of actually shooting this gun at paper to see what it does with the chokes. If it shoots well,I will keep it to save you more angst. If it shoots badly, you can have it back.

    Of course, if it shoots beautifully with those "jug chokes" you fear; you can then write down MORE figures on paper, and scratch your head until you have completely eliminated dandruff.

    Howzat?

    Sam Ogle, Lincoln, NE
     
  14. timb99

    timb99 Well-Known Member

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    Which computes because:

    18.4 mm = 0.724 inches

    18.3 mm = 0.721 inches

    18.6 mm = 0.732 inches

    Accouting for measurment accuracy, I think your barrel markings match quite well.

    You have no problem.

    Shoot some patterns.

    It'll shoot fine. Its a great gun. This is not a drawback.
     
  15. Hap MecTweaks

    Hap MecTweaks Well-Known Member

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    "The barrel reads .724 continous until reaching the choke tube then jumps up to .750 before entering the choke"

    How long is the .750 section prior to the beginning of the choke tubes, or is it the beginning of the tube? Is that measurement inside the choke tube itself? That's where the numbers become confusing in relation to the bores .724 figure.

    Hap
     
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