DUNKS Posted May 28, 2017 Report Share Posted May 28, 2017 Just getting back into shooting and have a proof mark question. I have asked Birmingham proof house but wonder if any of you guys are experts. Vintage Belgian 20g SXS. Original bore chamber marks are 20-70 in an omega on it's side. These marks are clear and have not been obliterated. The gun was originally proofed for Nitro! A later reproof "Birmingham" Shows marks in bold upper case 20-65 and the STD with crown above as standard proof. Can anyone suggest why the difference in chamber size. The chamber actual size is 72mm. Quote Link to comment Share on other sites More sharing options...
bruno22rf Posted May 28, 2017 Report Share Posted May 28, 2017 At a guess - the original marks are post 1924 and show the actual bore size/chamber length, the later proof marks show that it has passed proof for use with standard 2 1/2" cartridges? Only a guess though. Quote Link to comment Share on other sites More sharing options...
DUNKS Posted May 29, 2017 Author Report Share Posted May 29, 2017 At a guess - the original marks are post 1924 and show the actual bore size/chamber length, the later proof marks show that it has passed proof for use with standard 2 1/2" cartridges? Only a guess though. I accept this could be the case, but why would Birmingham not obliterate the unsafe 70mm mark? Will be interesting to hear what Birmingham have to say. If I get a reply! Quote Link to comment Share on other sites More sharing options...
wymberley Posted May 30, 2017 Report Share Posted May 30, 2017 I accept this could be the case, but why would Birmingham not obliterate the unsafe 70mm mark? Will be interesting to hear what Birmingham have to say. If I get a reply! If you do get a reply, please post. Have to say that your description of the marks doesn't seem to ring true except that the old Belgian provisional proof mark does sort of resemble omega on its side. Quote Link to comment Share on other sites More sharing options...
Guest cookoff013 Posted May 30, 2017 Report Share Posted May 30, 2017 maybe the chamber shrunk in the wash? Quote Link to comment Share on other sites More sharing options...
Gunman Posted May 31, 2017 Report Share Posted May 31, 2017 Chamber depth is measured with a plug gauge , some old guns had tighter chambers so the more modern plug will not go to the bottom so is proofed and marked at that depth . The submitter should have know this and opened up the chamber to a modern size . I have in the past found this regularly especially on older guns chambered for roll turn over cartridges [ much shorter cones ].and have re cut the chambers with a new CIP standard reamer as the tighter chambers sometimes caused ejection problems . How did you measure the depth ? The Proof Houses have been known to make mistakes although getting them to admit this was always a problem . There was no need to obliterate older marks as when reading proof marks the newer ones always supersede earlier marks . Quote Link to comment Share on other sites More sharing options...
DUNKS Posted May 31, 2017 Author Report Share Posted May 31, 2017 Thanks I will keep you posted. Quote Link to comment Share on other sites More sharing options...
DUNKS Posted June 5, 2017 Author Report Share Posted June 5, 2017 Mistake at the proofhouse. should have been marked 20-70 to match the chamber size. Quote Link to comment Share on other sites More sharing options...
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