doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Spanish gun proof?

I was looking at a few Spanish 20 gauges. I don’t know anything about Spanish guns, so I figured I would ask. The flats were marked for 20/70 chambers and 900 KGS. Is this proof level safe to use with modern American 2 3/4” loads?

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.
Kg/cm2 as determined by lead crushers is a different measure of pressure than BAR as determined by modern piezo transducers.
BAR was used only after the CIP standards were adopted about 1970

70 mm = 2 3/4"

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
1100 kg/cm2 proof = 15,645 psi for a service load of 10,430 psi + 10 - 14% or about 11,500 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

Thank you Drew!

Modern loads a are a hard no at 9500 psi service pressure.

Dave: Spanish guns came with one of these; 900 KGS 12g



Certainly a 2 3/4" 20g 900 KGS gun was intended to be used with 7/8 oz at 1200 fps loads; that's what I'd use, and be happy

Respectfully, and with no offense intended, I’ll raise an exception here.

Crusher pressure measurements are an expression of the total area under the pressure curve.

Transducer pressure measurements are an expression of the highest amplitude pressure observed.

In short, the two pressure measurement methodologies measure and describe different events. As such, there is no meaningful way to convert crusher measurements to PSI measurements and no meaningful way to convert PSI measurements to crusher measurements. Attempts to do so have a lot in common with trying to convert square foot measurements to linear foot measurements.

Understood Kyrie.
Just doing our best to provide meaningful guidance, and the 10 - 14% addition is generally accepted.

An explanation of the crusher technique is about 2/3 way down here
https://docs.google.com/document/d/1F2sQuPm05IE4VWYYnCkvuXmYEzQoWd_SQgaAfUOZEFU/edit

Major Sir Gerald Burrard published an estimated Lead Crusher (LUP) (Long) Tons/ Sq. Inch (TSI) to piezoelectric transducer Pounds/ Sq. Inch (PSI) conversion formula in the Third edition of The Modern Shotgun, 1955, Vol. 2 derived from simultaneous crusher and transducer pressure readings in a test barrel.
(Cp x 1.5) - .5 = TSI
TSI X 2240 = PSI

Hi Drew,

Not a problem friend. It's a complicated subject. An excellent, if technical, source is Sporting Arms and Ammunition Manufactures' Institute publications, especially this:

ANSI-SAAMI-Z299.2-Shotshell_Standards_2015-R2019-Approved-2019-04-23

We're all adults here, capable of making our own choices.

Good to see you posting, Kyrie.

Best,
Ted

Thanks Ted. I read but rarely feel a desire to post :-)

Best right back to you.

What Ted said Kyrie.

Would a 1970s Spanish double, of decent make, come with a hang tag and recommended loads?
What load would have been recommended for a 850 or 900 KGS 20g? 24 gm?
12g? 32 gm?
Thanks.