doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com 850 kg/cm sq Spanish proof (for the simple man)

The gun is a mid-1960s Pedro Gorosabel 16 ga., proofed at 850 kg/cm sq.

The questions are simple (but the answers may not be):

1) Can I shoot North American factory loads without a care?
2) Can I reload at 10,400 psi (published, Lyman's 5th) without a care?

I ask because 2 hours of internet reading still leave with me with information ranging from "shoot with confidence" to "Wait, stop!!!"

Thank you in advance, gentlemen.

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Thanks Colonel. In that case perhaps better that I change recipes.

Now can anyone explain why the same proof house (Eibar) would identify different proof pressures (e.g. 1000 kg/cm sq, 900 kg/cm sq, 850 kg/cm sq) to similar game guns (not "magnum proofed" guns) of similar era? All such guns seem to be stamped with the same 850 kg/cm sq (850 bar) proofmark.

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.
The CIP standards were adopted by Spain some time after 1969.

Under the Belgian Proof House revisions of 1924
16g and 12g guns were proved at 900 kg/cm2 for a 600 kg/cm2 = 8534 psi maximum SERVICE pressure;
20g were proved at 1000 kg/cm2 for a 670 kg/cm2 = 9530 psi maximum SERVICE pressure
+ 10 - 14% by piezoelectric transducer measurement
That would be a service of 2/3 of proof.

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

Those numbers are very similar to the British 3 tons = 850 kg/cm2 and 3 1/4 tons = 900 kg/cm2
850 kg/cm2 proof is equivalent to 3 tons service = 8938 psi (by transducers so 10 - 14% is not added)
900 kg/cm2 is 3 1/4 tons = 9682 psi
1000 kg/cm2 is 3 1/2 tons = 10,427 psi
1200 kg/cm2 is 4 tons = 11,917 psi

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" Peace of mind matters" and fingers count. If one of my period guns is safe to shoot, I now load to to basic pressure levels. For 12 bore I set my limit at 5,000 psi and 20 bore I set at under 8,000 based on service pressure levels for proofed guns. Sadly many old guns are marginal or truly not safe to shoot. But of mine which I feel are they get two basic loads at these modest pressures.

For 12 Bore I load 1 ounce shot at 1100 fps and 5,000psi or less. I can go as low as 3,800psi in this load, or push it up to 1250fps at 5,600psi. But nothing above that, as it fills in all my needs, at reasonable pressure levels. And they pattern very well as a bonus. All shells are trimmed down to proper length and marked as low pressure. Loads are tested or straight off Hodgdon and Alliant powder web sites.

16 bore are easy to load safely as the 16Bore.com data generated a lot of decent low pressure loads. I do not shoot many 16 guns any more but still have a good supply of loads on hand. All were very reasonable in pressure and gave about 1100-1150 fps which is fine for my needs.

For 20 bore I load two basic low pressure loads. A 7/8, 1150 fps load at 7,200 psi and a 3/4 ounce load at 1150 fps and 6,400 psi. These are in cut down shells. It is a bit harder to find low pressure load data for the 20 but you only need one or two if you think about it. I have known trap shooter use the same basic load for 30 years as well as others who seem to change their load every week like it is the shell not the shooter who is at fault for their misses.


All low pressure loads are marked with a single black magic marker line across the base and primer so that just at a glance I can confirm all my loads are low pressure.

When you cut down shells consider skiving the mouths to thin out the plastic. It makes crimping them easier as they can be thick when trimmed down. A brass Super crimp starting die makes nice deep crimp lines which seem to crimp well Also I noticed when I do this and have loads tested they always seem to have slightly lower pressures. I figure I can even get by with not trimming to exact length if the plastic mouth is real thin where it meets the forcing cone. So if I am off 1/32 or a 1/16" it is not big deal.

Thanks all for sharing. Very helpful!

I no longer load anything below about 7500 psi, 12 gauge or otherwise.
I keep the load reasonable as in 1 oz-1 1/8oz @ no more than 1200 fps, usually a bit lower, in 12 for protection of the wood, etc. If a gun is not capable of handling this pressure it's a "WALL HANGER".

With this in mind, I use the fastest powder that will give the desired load within that pressure. This keeps the peak pressure as close as possible to the breech with a rapid fall off as it goes to thinner sections of the barrel.

This has worked well for me over the years for any gun built after smokeless was regularly used. In the case of an earlier gun, say pre 1890 with very light breeches then I only shoot "Black".

Good grief! According to Randy Wakeman, I have a hand grenade.

"Using an 850 BAR proofed (or re-proofed at 850 BAR) shotgun it is the type of completely elective, completely unnecessary risk that no one should expose their sons, daughters, friends or neighbors to. Not everyone with one foot in the grave and the other on a banana peel has an untimely demise, but it hardly makes it an intelligent situation to decide to put yourself into. To subject others to this level of heinous, completely unnecessary risk is rude, thoughtless, and negligent. Friends don't let friends near 850 BAR proofed shotguns. If safety first is now less important than something else, just what is that "something else."