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bg55599

barrel micrometer

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    I am guessing you need the long shaft to see wear at any point in the barrel.

     

    If not, you can buy telescopic bore gauges from engineering suppliers which are T-shaped devices you push into a space and wind out to a touch fit. You then withdraw the gauge and measure with a normal caliper or micrometer.

     

    I have seen sets of four or five of those that'll go from 12mm to 150mm for less than 20 quid. However, the length on the shaft is usually only 150mm or so.

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    I bought one on ebay but it cost close to £200.

     

    They do crop up at local auctions from time to time and i'll keep an eye out for you.

     

    GB

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    I got the same one from Brownells last year along with the Gilchrist handle and reamer. Highly recommended. The bore micrometer gets a bit addictive though, everytime a mate changes a gun, you end up shoving the gauge down to check

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    In reply to John R, you use a bore guage to measure the diameter of the bore 9" in front of the breech to check that it is still in proof (or if you want to be absolutely correct - 'of proof'). Nominal diameter of a 12 bore at this point is .729" or 18.5mm. Of course if it has been lapped or polished out this measurement may be larger and if it is 10 thou or more larger, the shotgun has to be submitted for re-proof.

     

    You use a different instrument called a barrel wall thickness guage (much more expensive) to actually detect 'wear' or thickness in pits etc along most of the barrel length. As a general rule, minimum recommended BWT is 25 tho. Funny thing is that you can have paper thin barrel wall thicknesses and still be in proof 9" in front of the breech, so beware when buying used shotguns.

     

    C-B

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    In reply to John R, you use a bore guage to measure the diameter of the bore 9" in front of the breech to check that it is still in proof (or if you want to be absolutely correct - 'of proof'). Nominal diameter of a 12 bore at this point is .729" or 18.5mm. Of course if it has been lapped or polished out this measurement may be larger and if it is 10 thou or more larger, the shotgun has to be submitted for re-proof.

     

    You use a different instrument called a barrel wall thickness guage (much more expensive) to actually detect 'wear' or thickness in pits etc along most of the barrel length. As a general rule, minimum recommended BWT is 25 tho. Funny thing is that you can have paper thin barrel wall thicknesses and still be in proof 9" in front of the breech, so beware when buying used shotguns.

     

    C-B

     

    Good sence talked by Coney Basher, who obviously knows what he is talking about.

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