rovercoupe Posted September 29, 2018 Report Share Posted September 29, 2018 Odd question but do all 12 bore shotguns have the same bore diameter once you get past the chamber, forcing cone and before the choke at the end? Just my brain working overtime and cannot find a answer. Quote Link to comment Share on other sites More sharing options...
TIGHTCHOKE Posted September 29, 2018 Report Share Posted September 29, 2018 No. have you seen the thread on back bored barrels? Quote Link to comment Share on other sites More sharing options...
rovercoupe Posted September 29, 2018 Author Report Share Posted September 29, 2018 Nope I will have a search now, thanks Quote Link to comment Share on other sites More sharing options...
JohnfromUK Posted September 29, 2018 Report Share Posted September 29, 2018 There are differences, but once you are past the forcing cone, it is a 'nominal' 12 bore and near enough parallel until you get to the choke. Different makers have slightly different ideas about what '12 bore' actually is (0.729 inches was the old standard) and variations have been tried (like back boring), or even the "Vena Contracta", a Victorian idea with 12 bore chambers and 20 bore tubes! There is a good article here https://www.vintageguns.co.uk/articles/chamber-sleeving/ Quote Link to comment Share on other sites More sharing options...
rovercoupe Posted September 30, 2018 Author Report Share Posted September 30, 2018 Thanks, quite interesting that nobody can just decide on a nominal bore and just go with it! Quote Link to comment Share on other sites More sharing options...
Gunman Posted September 30, 2018 Report Share Posted September 30, 2018 As far as it goes 12 bore is >729" ,thats 18.5 mm to those of you who like that sort of thing . However there is a bore size tolerance that will range from >710" and >751" that will be within the 12 bore chamber range . Prior to CIP rules most guns produced in the UK used >719" or >729" as the norm . Continental guns tended to be >719" . Modern guns all tend to be >728"/18.5mm , There are exceptions to this with the so called back bored guns which in effect is boring out to a larger bore size of 18.8 mm for what ever reason and the argument is still going on as to whether this actually makes any difference to shooting other than as a sales gimmick . Quote Link to comment Share on other sites More sharing options...
wymberley Posted September 30, 2018 Report Share Posted September 30, 2018 18 hours ago, JohnfromUK said: There are differences, but once you are past the forcing cone, it is a 'nominal' 12 bore and near enough parallel until you get to the choke. Different makers have slightly different ideas about what '12 bore' actually is (0.729 inches was the old standard) and variations have been tried (like back boring), or even the "Vena Contracta", a Victorian idea with 12 bore chambers and 20 bore tubes! There is a good article here https://www.vintageguns.co.uk/articles/chamber-sleeving/ Flippin' 'eck, you can see how some poor unsuspecting RFD could get it in the neck for selling a 16 as a 20. Quote Link to comment Share on other sites More sharing options...
Gunman Posted September 30, 2018 Report Share Posted September 30, 2018 5 hours ago, wymberley said: Flippin' 'eck, you can see how some poor unsuspecting RFD could get it in the neck for selling a 16 as a 20. No all he has to do is read the proof marks . The nominal chamber size is quite clearly marked .The number 20/16/12 in a diamond . He should also have enough knowledge , and equipment to be able to measure a bore and to know from that . Quote Link to comment Share on other sites More sharing options...
casts_by_fly Posted September 30, 2018 Report Share Posted September 30, 2018 The mossberg ultimag guns are 0.779” for the 12 gauge and are, I think, the largest 12 bore gun bores on the market. rick Quote Link to comment Share on other sites More sharing options...
wymberley Posted September 30, 2018 Report Share Posted September 30, 2018 58 minutes ago, Gunman said: No all he has to do is read the proof marks . The nominal chamber size is quite clearly marked .The number 20/16/12 in a diamond . He should also have enough knowledge , and equipment to be able to measure a bore and to know from that . There was a smiley! Quote Link to comment Share on other sites More sharing options...
Lord v Posted October 1, 2018 Report Share Posted October 1, 2018 Said 20 16 is off to an extremely well regarded smith today for a chat about some fettling and possible re-blueing. (unexpected work bonus needs to be spent...) I'm kinda glad she's going down in PW legend already. Quote Link to comment Share on other sites More sharing options...
wymberley Posted October 1, 2018 Report Share Posted October 1, 2018 6 minutes ago, Lord v said: Said 20 16 is off to an extremely well regarded smith today for a chat about some fettling and possible re-blueing. (unexpected work bonus needs to be spent...) I'm kinda glad she's going down in PW legend already. You'll probably find me in the same place I'm guessing a little before noon. Quote Link to comment Share on other sites More sharing options...
Lord v Posted October 1, 2018 Report Share Posted October 1, 2018 I will keep an eye out. Quote Link to comment Share on other sites More sharing options...
wymberley Posted October 1, 2018 Report Share Posted October 1, 2018 1 hour ago, Lord v said: I will keep an eye out. If we ARE talking about the same place and the timing's right, I'm looking forward to seeing it. If you show me yours, I'll show you mine. Quote Link to comment Share on other sites More sharing options...
Lord v Posted October 1, 2018 Report Share Posted October 1, 2018 35 minutes ago, wymberley said: If we ARE talking about the same place and the timing's right, I'm looking forward to seeing it. If you show me yours, I'll show you mine. one up Heathfield I assume? Just look out for a fat Poirot. Quote Link to comment Share on other sites More sharing options...
wymberley Posted October 1, 2018 Report Share Posted October 1, 2018 4 hours ago, Lord v said: one up Heathfield I assume? Just look out for a fat Poirot. Yep, I kept an eye out for anyone walking in with a Midland PoW stock as I knew you hadn't been but I must have left before you arrived. Quote Link to comment Share on other sites More sharing options...
Lord v Posted October 1, 2018 Report Share Posted October 1, 2018 (edited) Yeah I didn't get there till 1 in the end. Annoying clients wanting me to do work. ********S. 29 minutes ago, wymberley said: Yep, I kept an eye out for anyone walking in with a Midland PoW stock as I knew you hadn't been but I must have left before you arrived. Edited October 1, 2018 by Lord v Quote Link to comment Share on other sites More sharing options...
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