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Sidelock
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What is the CIP minimum EOC for a 20ga with good quality modern steel barrels.

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Commission Internationale Permanente pour l'Epreuve des Armes à Feu Portatives (C.I.P) http://www.cip-bobp.org/
Standard CIP proof pressure of 850 kg per sq. cm. (BAR) = 13,920 psi for a service pressure of 10,730 psi
Shotgun recommended minimum wall thickness for Category 1 “Standard Steel” (Non-alloy AISI 1045) with tensile strength = 101,526-123,137 psi

10 & 12g...........................20g
End of chamber - .079”........0.075”
4” from breech - .075”.........0.071”
8” - .043”.........................0.041”
12” - .030”.......................0.028”
16” - .024”.......................0.022”
20” - .022”.......................0.020”

Category 2 (Non-alloy AISI 1060) and 3 (Alloy with 3% Chromium and 2% Molybdenum) with a Tensile Strength of 116,030 - 159,396 psi
10 & 12g End of chamber - .063”
20g - .059"


The Hunter's Encyclopedia, Raymond R. Camp Editor, 1948
From the German proof house: minimal wall thickness at the end of chamber, regardless of length, for 12, 16 & 20 gauge guns should be 2.3mm (.0906”) for “Ordinary Good Steel”; 2.1mm (.0827”) if a “Special Steel”.


Category 1 would fit the industry standards for 4140 & 4340 - both are "low alloy" steel
AISI 4140 Chrome Moly
Carbon - 0.38 - 0.43%
Manganese - 0.75 - 1.0%
Nickel < .01%
Chromium - 0.8 - 1.1%
Molybdenum - 0.15 - 0.25%
Ultimate tensile strength - 95,000 psi

AISI 4340 Chrome Moly Nickel
C - 0.38 - 0.43%
Mn - 0.6 - 0.8%
Nickel - 1.65 - 2.0%
Cr - 0.7 - 0.9%
Mo - 0.2 - 0.3%
Ultimate tensile strength - 108,000 psi

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[Linked Image from i.goopics.net]
Salut,
L'épaisseur des tubes son dans son dans les clous de la CIP.

1 member likes this: Drew Hause
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Sidelock
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Here it is in American, with mm converted to inches wink bis89 = 3 1/2" would be the end-of-the-chamber

[Linked Image from photos.smugmug.com]

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Boxlock
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Boxlock

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This is some great information, it looks like my barrel would be fine if it were category 2 material but definitely doesn’t meet the category 1 numbers. Is there any chance the material could be category 2 based on age and manufacturer? Or is that unlikely?

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I'm sorry but highly unlikely if proved at 1000 kg/cm2

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Sidelock
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Sidelock
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So we are looking at .006 less than what we expect to see. That could have been removed when they were struck for final finish. I was told that many of the 2" barrels were proofed, then had more metal removed before finish and that would often drop them down to near .020 or less in some cases. Once they passed proof as long as the internal bore was not altered to take it out of proof nobody worried about much it seems.

May I ask what tools you are using to measure your wall thickness and how much confidence do you have in their accuracy? It sounds like you are getting very good results.

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Boxlock
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Boxlock

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I’m using a homemade tool that works the same as the one shared in this thread: https://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=629196#Post629196 I’m pretty confident to within a thou or two.

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Sidelock
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I don't understand your math Jon
If we expect the end-of-chamber WT to be .090" (or greater) and it is now measured at .065" that would be .025" less, or > 25% less.
.020" in the distal 1/3 of the barrel is IMHO not an issue (other than dent risk); inadequate end-of-chamber WT is an entirely different risk.

Not having much luck regarding the barrel steel used on the No. 3 in the 80s.

The No. 1 was reported here to have "Chrome Nickel steel" in 2008
https://www.thefield.co.uk/reviews/review/aya-no-1-shotgun-review

https://www.thefield.co.uk/news/aya-no-2-20-bore-de-luxe-46431 2021
The No. 2 has Bellota EC4 = British EN8 = AISI 1040 - 1045
The No. 1 Bellota URKO-035 AISI 4135 Chrome Moly (not Chrome Nickel), steel shot proved at 1370 BAR
https://mecanizadosespeciales.com/ACEROS.htm

In general, the No. 3 was a game gun. What is the overall weight?

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Sidelock
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Originally Posted by Drew Hause
What is the overall weight?

No 3 and 4 20 bores usually a little under 6 lbs for a typical stock length and density.

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