doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Actual Bore Proof Size vs Measured Size

Hi there everybody, i recently acquired a gun with 18.4 proof stamps. The gentleman that sold me the gun has been in possesion for a long time and he tells me no work has been done on barrels. My bore gauge 9" from the breech measures as .728. Is it possible to have that tolerance up to .728 bore size for a 18.4 stamped bore?

Best regards,

Kem

A plug gauge is used to measure the bore at 23 cm = 9".
18.4 would be .724 to .727" - ie the 18.5 gauge of .728" would not pass.
The British Proof House is never wrong, but .001" may be close enough

You can't put a .728" peg in a .728" hole, proofed correctly.

Thanks Drew, maybe my micrometer is not sensitive enough. Is there a digital bore gauge that you can recommend?

Regards,

Kem

I use a ball gauge Kem, and .001" is close enough for me.

Thank you Drew, much appreciated for your help.

Best regards

If its marked ay 18.4mm which in fact is .724409"then it goes out of proof at 18.6mm or .732228".
When boring for proof you needed to bore to to .725" effectively to accept a 18.4 mm plug .( you can not put a 18.4 mm plug in a 18.4mm hole without a hammer )
Proof Houses have , in my experience been at times very strict ,so if the barrel would not take an 18.5mm plug it would have been marked as 18.4 mm
In other times they have been a little lenient and marked up in this case at 18.5mm .
That said after 2010 with yet more CIP rules ( another story here ) and getting new gauges to comply with these rules they did become very strict on bore sizes and chamber depths .
To those of us who did submit guns for proof , new barrels as well as reproofs it did become a bone of contention , not to mention a headache trying to figure out why for no reason all our cutters and gauges were no longer " acceptable ".

As Drew says the Proof Houses are never wrong . Even when they are and in my personal experience they can be and have been .

Thank you very much now i have all the answers to my questions. I was really thinking why a gun marked 18.4 and never been messed with measures .728. Now i know why.

Best regards

Thank you for that clarification gunman. Don't forget "the Proof House is never wrong."

Could you please comment?
Could barrels be lightly honed, say .729" to .732", remaining in dimensional proof, and not then be reproved? Does removal of any metal require reproof?

2006 Proof House Rules
https://www.gunproof.com/downloads/rules-proofing
p. 7
"... if a Barrel of the First Class, be enlarged by more than 0.2mm (.00787") beyond the size marked and thereby be reduced in Substance or Strength, thereby rendering the Proof Marks invalid, such Barrel shall be deemed to be out of Proof and Unproved.