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Joined: Mar 2011
Posts: 4,080 Likes: 466
Sidelock
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OP
Sidelock
Joined: Mar 2011
Posts: 4,080 Likes: 466 |
Did British gunmakers adhere to .729" for 12 ga. or was there a range? Is there anything in these proof marks to suggest exact diameter? Does the diamond with 12 and "c" in it have significance other than gauge or range of manufacture from 1925-1954? Thanks. Gil 
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Joined: Dec 2001
Posts: 6,992 Likes: 402
Sidelock
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Sidelock
Joined: Dec 2001
Posts: 6,992 Likes: 402 |
12 C inside the diamond along with the 2" tells you it has a standard 2" 12 bore chamber.
The bore diameter is marked as 12, meaning at 9" forward of the chamber it would accept the 12 bore plug gauge but not the 11 bore plug.
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Joined: Feb 2013
Posts: 168 Likes: 57
Sidelock
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Sidelock
Joined: Feb 2013
Posts: 168 Likes: 57 |
I have an older 12 gauge Birmingham shotgun 1904-1925 proofs marked 13/1, so there must be a range? What does the 13/1 signify?
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Joined: Dec 2001
Posts: 6,992 Likes: 402
Sidelock
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Sidelock
Joined: Dec 2001
Posts: 6,992 Likes: 402 |
13/1, I am going from memory, means the original bore diameter would take the 13/1 plug(.719) but not the 12 plug(.729).
Steve
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Joined: Jan 2006
Posts: 9,415 Likes: 313
Sidelock
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Sidelock
Joined: Jan 2006
Posts: 9,415 Likes: 313 |
Gauge was marked starting with the 1855 Rules of Proof Bore dimensions and marks post-1887 Rules of Proof "At proof if a plug gauge of 0.729" diameter (but not one of 0.740") will enter the bore to a depth of 9", that barrel would have been marked 12."  Bore was marked in metric starting in 1984 to the 1889 Revisions.
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Joined: Mar 2011
Posts: 4,080 Likes: 466
Sidelock
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OP
Sidelock
Joined: Mar 2011
Posts: 4,080 Likes: 466 |
Thanks, Steve, so is another way of stating what you said is 11" from breech on a 2" chamber a 12 ga. plug would fit, but not a 11 ga.? Or is it 9" forward of the breech? Gil
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Joined: Jun 2012
Posts: 119
Sidelock
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Sidelock
Joined: Jun 2012
Posts: 119 |
No. The measurement is taken 9" from the breech. Chamber length is not a factor.
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Joined: Jun 2012
Posts: 119
Sidelock
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Sidelock
Joined: Jun 2012
Posts: 119 |
A bore marked 12 measures between .729" - .739"
A bore marked 13/1 measures between .719" - .728"
A bore marked 13 measures between .710" - .718"
Gunmakers would generally bore the barrels in the low to middle of the range so there is room for honing without the need for a re-proof. This is not always the case though.
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Joined: Dec 2001
Posts: 6,992 Likes: 402
Sidelock
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Sidelock
Joined: Dec 2001
Posts: 6,992 Likes: 402 |
Blue Grouse is correct, my mistake.
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Joined: Dec 2001
Posts: 6,268 Likes: 200
Sidelock
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Sidelock
Joined: Dec 2001
Posts: 6,268 Likes: 200 |
I have seen doubles with one barrel stamped 12 and the other stamped 13/1. One of these was a Boss, so the difference must not have been considered a lower standard.
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