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Joined: Dec 2006
Posts: 1,531 Likes: 20
Sidelock
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OP
Sidelock
Joined: Dec 2006
Posts: 1,531 Likes: 20 |
Is there a table somewhere that lists the ranges for each of the bore diameter markings? I'm looking at a gun marked 13/1 and I don't know what that means it was originally nor does it allow me to determine whether it's still in proof given the current bore diameter measurement.
Thanks.
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Joined: Jun 2008
Posts: 2,768 Likes: 115
Sidelock
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Sidelock
Joined: Jun 2008
Posts: 2,768 Likes: 115 |
It would have measured between .719" and .729" at time of Proof. So, it will be out of Proof in British terms if is goes over .729" at 9" from the breech face. Hope that helps. Lagopus.....
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Joined: Dec 2006
Posts: 1,531 Likes: 20
Sidelock
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Sidelock
Joined: Dec 2006
Posts: 1,531 Likes: 20 |
Thanks. That's just what I needed to know.
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Joined: Mar 2005
Posts: 709
Sidelock
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Sidelock
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Joined: May 2007
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Sidelock
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Sidelock
Joined: May 2007
Posts: 605 Likes: 1 |
.710"-.719" is 13/1, not 13... but it depends when it was proofed, because of the introduction of the intermediate bore sizes (when? haven't my refs to hand...); so .710"-.729" is 13 too...! I think...
Edit: getting myself mixed up and will now await correction from a credible source!
Last edited by cadet; 09/17/12 05:28 PM.
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Joined: Jul 2010
Posts: 707
Sidelock
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Sidelock
Joined: Jul 2010
Posts: 707 |
I thought: 12/1 is .740 12 is .729 13/1 is .719 13 is .709 I'll assume I'm right until a Brit on the forum quotes the proof house to debunk me. 
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Joined: Mar 2003
Posts: 184
Sidelock
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Sidelock
Joined: Mar 2003
Posts: 184 |
Here is a handy little reference.... 
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Joined: Mar 2005
Posts: 709
Sidelock
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Sidelock
Joined: Mar 2005
Posts: 709 |
Right when I thought I was getting the hang of this stuff.
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Joined: Dec 2001
Posts: 12,743
Sidelock
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Sidelock
Joined: Dec 2001
Posts: 12,743 |
As best as I recall the inbetween sizes were started with the proof rules of 1887, so yes prior to that a 13 could have been from .710" to .729" A 13/1 would of course have never been other than .719"-.729"
Gauge diameters are calculated to the nearest .001". The in-between sizes depending on whether there are 1 or 2 steps are either half way or 1/3-2/3 of the difference between gauges. On these any numbers beyond 3 decimal places are simply dropped even if .0005" or above. Thus .710" + .729"/2 = 1.439"/2 = .7195". The .0005 is dropped so the 13/1 is listed in the proof charts as .719". In this case if you calculated 13/1 as a 12˝ gauge it would figure to .7193" but this is not the case for all gauges & especially with the gauges having two steps.
Miller/TN
I Didn't Say Everything I Said, Yogi Berra
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Joined: Dec 2006
Posts: 1,531 Likes: 20
Sidelock
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Sidelock
Joined: Dec 2006
Posts: 1,531 Likes: 20 |
Thanks. I love how much knowledge is available on this board and the willingness of those who possess it to share it freely.
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