16ga.com ~ View topic - Conversion tables, Proof, and Pressure Information

(This comes out alot better from Word or an e-mail. If you want me to e-mail you the text, PM or e-mail revdoc2@cox.net )

PROOF/PRESSURE

British proof markings: The "tons" mark (which is service pressure) was not used until 1954. Between 1925-54, the chamber length was marked. 1904-1925 guns would not have the chamber length, but only the shot charge and a nitro proof.
http://www.gunproof.com/Proofing/proofing.html

Information about the Birmingham Proof House
http://www.basc.org.uk/media/100_proof.pdf

There are three pressure measurement systems (lead crushers/LUP, copper crushers, and piezo), and two standard systems of measure units (USA/SAAMI and CIP/British/European) and two differing units (psi and tons and bar and Kg/Cm sq) within each system, different proof laws by country, and differing proof laws by age.
Unfortunately, there is essential NO formula to convert BAR expressed as LUP (CIP) to PSI (SAAMI). LUP + 1000 does not reliably predict the actual piezoelectric transducer measured pressure.
In 1989, all proof data was marked in metric using the BAR as the unit of measurement. The use of TONS per sq. inch was dropped. Under this system, 850 bar represented standard proof, with 1200 bar being special or magnum. 2 1/2" chambered guns are usually proofed 850 bar
2 3/4" chambered may be proofed 900 bar (3 1/4 tons per sq. inch) or higher.

**650 bars is standard CIP (British and European) service pressure for shells designed for guns proofed at the CIP standard of 850 bars**

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

Per the 1954 Rules of Proof, here are the equivalent service pressure values:
3 tons--8,938 psi
3 1/4 tons--9,682 psi
3 1/2 tons--10,427 psi
4 tons--11,917 psi
These numbers SHOULD apply to guns proved under the 1925 rules, which were stamped only with chamber length and shot charge. Thus, a 2 1/2" chambered gun, 1925 rules of proof, would be equivalent to 3 tons; a 2 3/4" chambered gun to 3 1/4 tons.

A service pressure of 3 tons per sq. in. = 8,938 psi service pressure (SAAMI)

For comparison, here's data from actual pressure testing:
3 Dr.Eq. 1 1/8 oz. Winchester Trap Load1,202 fps 9,600 psi
Winchester AA Xtra-Lite 1 oz WAAL12
1189 fps 8000 psi

Standard 1900s loads per LC Smith Hang Tags:
12g 3 dram 1 1/4 oz 1165 fps
16g 2 1/2 dram 1 oz 1165 fps
20g 2 1/4 dram 7/8 oz 1155 fps

The 12g 2 5/8" 1 1/8 oz. 3 1/4 Dram Eq (1295 fps) load of the 1920s ran about 10,500 psi.
The Super-X 2 3/4 inch 3 3/4 dram equiv. 1 1/4 ounce load (1330 fps) was near the SAAMI max. of 11,500 psi.

Baschieri & Pellagri data BUT you must add 500-1000 psi to the reported pressure to get an approximation of the SAAMI equivalent PSI. The 16g F2 Classic is factory listed at 9,867 psi but testing by Tom Armbrust showed it to be 10,500.
http://www.bandpusa.com/files/db_trio.pdf

Gamebore Traditional Game 16g 28gm (1 oz.) is reported to run 1260 fps at 8122 psi but pressure testing by Tom Armbrust showed it to be 8400 psi. The box is labeled "These cartridges are suitable for use in:
70mm case length: Guns with a chamber length of 2 3/4" or longer, nitro proofed to a service pressure of 3 1/4 tons per square inch (900 kg per square cm)
67 mm case length: Guns with a chamber length of 2 1/2" or longer, nitro proofed to a service pressure of 3 tons per square inch (850 kg per square cm.)"

It's appropriate to view the 3 ton/650 bar/8,939 psi pressure as the maximum service/using pressure rather than the standard/recomended service pressure. The Gamebore loads run below 8500 psi but are 'approved' for use in 3 ton/650 bar service/850 bar proof guns. In light of the age of the wood and metal of classic American and British SxSs, shoot low pressure to save the action, shoot light shot charge/low velocity to spare the wood. It seems reasonable to limit pressure to 8,500 psi, and several commercial loads are available from 5,000- 7,000 psi http://www.doublegunshop.com/forums/ubbt...ge=11#Post31805

BOTTOM LINE: ANY 850 BAR (proof) = 650 BAR service or 3 TON service gun should be fine at pressures under 8500 psi, or 3 1/4 tons less than 9,500 psi.

ANSI/SAAMI Shotgun Pressure Specifications (Maximum Average Pressure in PSI)
All Piezo measurements unless specified)

Cartridge Maximum Average pressure
10 gauge 11,000 (all)
12 gauge 11,5000 (all but 3 1/2" mag)
12 gauge 3 1/2" mag 14,000
16 gauge (11,500 (all)
20 Gauge 12,000 (all)
28 gauge 12,500 (all)
.410 Bore 2 1/2" 12,500
.410 Bore 3" 13,500

WEIGHT

1 ounce = 0.0625 pound= 28.35 grams

24 gm=.85 oz.=just less than 7/8 oz.

26gm=15/16 oz.

28 gm=1 oz.

30gm=1.06 oz.=1 1/16 oz.

32 gm=1.13 oz.=1 1/8 oz.

34 gm=1.2 oz.=1 1/5 oz.

36 gm=1.27 oz.=just more than 1 1/4 oz.

SHOT SIZES

US UK Italian

mm inches mm inches mm inches

4 3.3 .13 2.8 .11 3.1 .122

5 3.0 .12 2.67 .105 2.9 .1145

6 2.8 .11 2.54 .10 2.7 .1065

7 2.54 .10 2.4 .095 2.5 .0925

8 2.3 .09 2.29 .09 2.3 .091

UK

http://www.kwacs.org.uk/barrels&choke.htm
http://www.hrwscothunt.ndtilda.co.uk/info/data.htm

From the Eley Shooter's Diary, 2005:

British 4 3.1mm, .12", 170/oz

5 2.8mm, .11", 220/oz

6 2.6mm, .10", 270/oz

Italian

http://www.bandpusa.com/files/productguide-USA-2005.pdf

Member Joined: 08 Nov 2005 Posts: 3438 Location: Illinois

The only bars in this part of Illinois are they ones selling cold refreshments-- Twisted Evil

Sorry

couldn't help that the info is great for future refence Wink

*Last edited by revdocdrew on Sun Apr 01, 2007 8:30 pm; edited 1 time in total*

We're at it again on DoubleGunBBS and I have significantly revised the first post conversion tables and infro

Member Joined: 09 Dec 2005 Posts: 989 Location: Las Vegas

Rev: What's the difference between "proof" pressure and "service" pressure? If a particular load has a pressure of 9,000 psi, is this "proof" or "service" pressure?

Matt

That's pretty important Matt and I think I've at least got that part into my pea brain. All those pressures I've reported, and the 16g reloading group has from Tom Armbrust, and that ammo makers publish are USING pressures or service pressure or the pressure of shells for which the gun was originally designed-PROOF pressure is (in general) about a third greater than service pressure.

Member Joined: 09 Dec 2005 Posts: 989 Location: Las Vegas

AHHHHHHH! Thanks Rev! Even I get it!

Matt

Guys-we're still wading through this extremely murky water over on DoubleGunBBS http://doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=33387&page=1#Post33387
This is really important for those of us shooting 'classic' American (my 'youngest' is 94) or even modern British guns.
Bottom line-there is no reliable way to convert the old British LUP to modern transducer SAAMI psi. I'm still trying to find out what (modern number) psi these old guns were designed for Confused

although one can safely say that it is wise to keep the pressures below 8500-9000; and with a 12g it's pretty easy to keep it below 7000.

I hope the 'final word' is now on the first post 'Conversion Tables and Information' Rolling Eyes

Joined: 01 Jul 2006 Posts: 26 Location: Finland

You might find this information useful also. The official C.I.P. definitions for different shotgun calibers (pdf-document):

http://www.intermin.fi/intermin/images.nsf/files/DA1ED40B966A1173C2256FBE002E6A2E/$file/HAUL+VII+haku+02.pdf

And the official C.I.P. maximum shell sizes and minimum chamber sizes for shotgun calibers (Caliber 4 is pretty impressive Smile

:

http://www.intermin.fi/intermin/images.nsf/files/DB4FF73D9BB95EB6C2256FBE002E8598/$file/TABVIIcal.pdf

The pressures in the table are explained on the bottom of the page, PTmax is, as I understand it, the maximum recommended nominal pressure. The average pressure used during proofing, PE, is about 30% higher, as noted earlier in this thread.

Please note also, that the shell lengths 65mm (2 ½") and 67.5mm (2 5/8") are the same from the C.I.P safety point of view. I shoot 2 5/8" shells in my 1928 16 ga. A5 with a 2 ½" chamber. They just barely have enough space to be thrown out the exit.

I just spoke with Tom Armbrust about actual pressure/speed testing of turn-on-the-century and post-WWI loads. Mike Campbell generously offered to supply some old shells for testing. This was not a new idea (surprise Rolling Eyes

) and basically doesn't work (as Bro. Larry suggested in an e-mail.)
There were lots of shells makers back then with little uniformity beyond the reported Dram Eqivalents, and few had the capacity to perform any kind of pressure testing. His previous efforts with old shells showed markedly diminished speeds because of deterioration of the primers (if they detonated at all) and powder AND an increase in pressure as the paper case and fiber wads dried out and became less compressible. So much for that great idea Confused

He also confirmed that pressure reported by British and European manufacturers (CIP) is significantly less than when measured by piezotransducer (SAAMI) apparatus. Moderate pressure loads may only be 500 psi greater, but higher pressure loads, esp steel, can be thousands higher. Shocked

Much thanks to Tom for graciously sharing his expertise!

I think the wisest advice you gave here already Rev, is to go easy in both pressures and velocities on the older classic double guns. I would add limit the shot charge weights to an ounce or less too. The lower the recoil, the better for the older guns.

If you must shoot high pressure, high velocity ammo, or heavy shot charges, get a stoutly made modern gun for that--like a 16 ga Citori or a good pump gun made in the post WWII era. These guns will handle anything you can reasonably and sanely stuff in them and will do so for your whole life. By the time the wood on them is old and brittle, we will be too. Wink

Based on this new information Bro. Larry just received from the Birmingham Proof House, I edited the original post:

Per the 1954 Rules of Proof, here are the equivalent service pressure values:
3 tons--8,938 psi
3 1/4 tons--9,682 psi
3 1/2 tons--10,427 psi
4 tons--11,917 psi
These numbers SHOULD apply to guns proved under the 1925 rules, which were stamped only with chamber length and shot charge. Thus, a 2 1/2" chambered gun, 1925 rules of proof, would be equivalent to 3 tons; a 2 3/4" chambered gun to 3 1/4 tons.

Member Joined: 15 Feb 2006 Posts: 135 Location: Anchorage

This is great information, but I have one thing that confuses me. The information shows a service pressure for the 850 Bar of 10,700. The 850 Bar was I thought generraly equivalent of a 3 ton proof. The list then shows a lower sevice pressure of 9682 for the 3 and1/4 ton proof which is I believe considered to be like 900 Bar. It would seem the sevice pressure should be higher on the 3 and 1/4 ton that on the 850 Bar so I am wondering if someone can explain what I am missing.

I am particularly inereted because I have one British side by side gun that is 2 and 3/4 inch chambered and proofed at 3 and 1/4 ton. I want to get a reasonable grasp of what commercial load it will safely shoot. Thanks.

Trigg

Quite right Trigg and there is an extensive discussion on this thread:
http://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=33387&page=17&fpart=1
Larry understands this much better than I, but I interpret all this to mean that the SAAMI psi conversion for the 1954 TONS measurement is different from the 1989 BAR measurement Rolling Eyes

Bottom line: ANY 850 BAR or 3 TONS gun should be fine at pressures under 8500, or 3 1/4 tons less than 9,500 psi