Hi I am a new member and have been studying all the information on this site about evaluating used guns for safety. I have just acquired a 20ga AYA #3 manufactured in 1983. The gun is proof marked at 1000 Kp/cm2. The bores measure exactly as marked at 15.9mm and the chambers measure a normal size per CIP tables, the chokes seem original. The barrel wall thickness of the thinnest barrel measures 0.065” at the end of the chamber, 0.065” at the end of the forcing cone and 0.043” at 9” from the breech. The original barrel weight was marked at 1080 grams. I’ve weighed the barrels and they are currently 1067 grams. I’m baffled were the 13 grams of material went.

I’m wondering if I should be concerned at all or just use the gun and enjoy it. Thanks for any advice.

Welcome on your first posting

Initial weight, some work need to install and contour
Should stay within 98% of the stamped weight

Use it and enjoy it

https://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=363428

Thank you for the welcome. Are you saying that the stamped weight isn't necessarily the weight as final assembled? I had assumed the proof was done with the barrels fitted to the action. I guess if I were in the manufacturing business I would want the proof done before I invested production time in the final finishing?

https://thefiringline.com/forums/showthread.php?p=6910526

https://www.shotgunworld.com/threads/another-proofing-question-sorry.487104/

Two possibilities. First the barrels have been refinished at some point and your metal loss occurred then. Second possibility is they were struck lighter after the proof and then finished. I vote for the second. Either way it sounds to be in great shape for shooting.

What KY Jon said... ^^^^^^^

Did you really mean .065" at the forward end of the chamber?!?
The CIP "standard steel" 20g minimum would be > .075", and most smiths recommend > .090"
Are the chambers marked 70mm and now measure 2 3/4"? If someone lengthened the forcing cones, and the chambers slightly in the process, that might explain the barrel weight discrepancy.
You are correct that the weight is stamped at the time of proof. Belgian proof was after final fit and finish. I couldn't find what the Spanish proof house process was.

BTW: Spanish 1000 kg/cm2 proof = 14,223 psi + 10-14%, for a service load of about 10,500 psi

Any chance the chamber was altered?

I took some more measurements and made a mould of the chamber to better understand the shape of the forcing cone. A plug gauge of 0.685” diameter inserts 71mm into the chamber. This is the middle of the CIP length range using the minimum diameter gauge from what I see on their tables. The forcing cone length is 0.42”. Bore diameter at the end of the forcing cone is 0.632” which is less than the CIP max of 0.637 and only slightly more than the main bore diameter. I remeasured the wall thickness and the thinnest spot is on the top of the right barrel closer to the rib. Left and right barrel wall thickness are as follows:

End of chamber left=0.070”, right=0.065”
End of forcing cone left=0.85”, right=0.78”
Another 0.625” down the barrel left=0.070”, right=0.065”

It would seem to me the chambers are original, the right chamber is closer to the top of the barrel, eccentric by about 5-10 thou.

If the outside of the barrels were refinished it was well done, the barrels profile is very nice and smooth.

Does anyone have any hints on how to tell if the barrels might have been re-profiled? This gun came from Europe through an importer of surplus guns. From what I understand I can’t imagine this gun would have been worth the expense to do that kind of thing to restore. The stock looks like it was refinished and I think someone cold blued the barrels to cover some bluing wear on top of the barrels.

Thanks everyone for taking an interest.

My compliments on your careful evaluation obuerkle, which should serve as both an example and warning to everyone
There is a good collection of end-of-chamber wall thickness measurements here, and none measured < .084"
https://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=615227

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

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

Salut,
L'épaisseur des tubes son dans son dans les clous de la CIP.

Here it is in American, with mm converted to inches bis89 = 3 1/2" would be the end-of-the-chamber

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?

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

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.

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.

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?

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

1.9mm is .0748. Does the drawing above not call for 20 bore at chamber to be 1.9 then drop to 1.8 which is .071? 2.0mm is the 12 measurement which is .0787. We have arbitrary picked .090 or .100 as a benchmark. I have never seen it documented.

The overall weight of the gun is 6lbs-2oz, someone added a rubber recoil pad at some point so that might be adding a little weight. I have reached out to AYA USA and they said they would contact AYA in Spain their opinion. I’m not feeling too optimistic but it will be nice if they can give some info. I’d be surprised if they could use a high strength steel for barrels and also attach ribs and keep the required heat treatment.

better safe dan sorry...

don shoot hit...

Thank you ed for your insight.

It would be a great addition to our wall thickness data if you would please document the end-of-chamber wall thicknesses of your Army & Navy, William Evans, W&C Scott, and Cogswell and Harrison sidelocks, and those of your recently acquired English boxlocks. Have you listed them for sale yet BTW?
Please include the maker, gauge, proof level, and overall weight (light weight game guns would be expected to have thinner barrels). It would be very helpful if you'd include the MWT and location thereof.
What wall thickness gauge do you use ed? Or who does the measurements for you?
What wall thickness information do you provide to potential buyers...so they can be safe rather than sorry?
I assume you accept returns if on repeated measurement by the purchaser the numbers are less than your 90/30?
Thank you.

Rev Drew,
Good morning.

Would you confirm the numbers from your post above?

Standard CIP proof pressure of 850 kg per sq. cm. (BAR) = 13,920 psi for a service pressure of 10,730 psi

That would mean a gun with a 900 bar proof would be 14739psi for a service pressure of 11348psi?
In 12ga that would be 152psi off of saami's 11.5k?

Thanks!
Bill

Here you go Bill

https://bobp.cip-bobp.org/en/tdcc_public?page=1&cartridge_type_id=7
12g 50mm, 65mm, and 70mm “Standard Proof” lead or steel (limited to no larger than 3.25 mm and max. fps 1,300).
Numbers are transducer BAR converted to PSI.
Maximum Average (SERVICE) Pressure 740 BAR = 10,733 psi;
Maximum Statistical Individual Pressure 850 BAR = 12,328 psi
Mean PROOF Pressure 930 BAR = 13,489 psi

12g 3” & 3 1/2” “High performance/Superior Proof”
Maximum Average (Service) Pressure 1050 BAR = 15,229 psi
Maximum statistical individual pressure 1200 BAR = 17,405 psi
Magnum proof 1320 BAR = 19,145 psi

Both 65 and 70 mm 16g standard is SERVICE 780 BAR or 11,313 psi;
MSIP 900 BAR or 13,053 psi;
PROOF 980 BAR or 14,214 psi.

Both 65 and 70 mm 20g standard is SERVICE 830 BAR or 12,038 psi;
MSIP 950 BAR or 13,779 psi;
PROOF 1040 BAR or 15,084 psi.
(The original chart from 1984 and revised in 2000 indicates 20g PROOF 1080 BAR or 15,664 psi. The number was revised to 1040 BAR 11-2021.)



Spanish Service Loads Pre - CIP c. 1970
850 kg/cm2 proof = 12,090 psi for a service pressure of 566.6 kg/cm2 or 8060 psi BUT as measured by lead crushers, so by modern piezo transducers the pressure would be + 10 - 14% or about 9000 psi
900 kg/cm2 proof = 12,801 for a 600 kg/cm2 = 8534 psi service pressure + 10 – 14% or about 9500 psi
1000 kg/cm2 proof = 14,223 psi for a service load of 9,473 psi + 10 – 14% or about 10,500 psi
1200 kg/cm2 proof = 17,068 psi for a service load of 800 kg/cm2 = 11,380 + 10 – 14% or about 12,500 psi

850 kg/cm2 proof was commonly used for entry level Basque 12/70 guns of the 50's through the early 70's. Better grades carried 900 or 1000 kg/cm2 proof with some 12/70 pigeon guns 1200 kg/cm2.

Perfect!!!
Those are the numbers I remember.

Thanks.
Bill

Not relevant to the subject gun, but for future assistance, I found this:

2007 in response to a question regarding use of steel shot
"Our guns in standard aren´t tested for steel. Guns are only tested for steel when is required by customer and in that case is stamped in barrels with a fleur de lis."
Regards. AYA-AGUIRRE Y ARANZABAL, S.A."

https://www.shotgunworld.com/threads/are-new-ayas-steel-shot-rated.144024/
Since 2012, all AyA shotguns have been proofed for High Performance Steel and are stamped with the Fleur-de-lis.
I have an AyA manufactured in 2009. I wrote to AyA and asked if there was a qualitative difference between barrels made in 2009 and barrels made in 2012. Here is the answer I got, verbatim:
"Some technical specifications always changes (sic). Our advise (sic) is to use cartridges under tested proof."

This lists only the No. 56, 37 & Augusta with "Chrome Nickel Steel"
https://doublegunshop.com/aya2.htm
https://doublegunshop.com/aya3.htm