doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Heuse-Riga Fils?

Dr. Drew:

Wall thickness and the absence of corrosion are non-negotiable items for me when it comes to using any braided steel barrel. But...if a gun is sound and has adequate minimum wall-thickness (say 25k and up), then I have no qualms about using it. I've owned and hunted with 3 Damascus doubles now (2 English, 1 American) and once I was satisfied as to the soundness of the tubes, I never gave it a second thought. Use adequate loads (8,000 psi and below) and observe the required care and cleaning regimens and you should be golden.

From (finally!) going through all the data you so generously provided, I have the following summary:

2Bar Crolle-type Damascus 54k Tensile strength
ANSI 1020 (early fluid steels) 61k
Krupp Fluid steel 85k
4140-type steels 95k
Winchester Nickel steel 100k
Winchester Proof steel 115k

(The Winchester Nickel steel was something of a revelation. No wonder those guns never wear out.)

What this summary does for me is that it confirms the immense level of protection (overkill, which largely results in excessive weight) built into most mass-produced firearms. If you use RST-type, low-pressure shells (which perform flawlessly for me in the uplands) you'll never even get close to the tensile limits of even a mediocre Damascus gun. If you happen to get an obstruction in the barrel, even the best fluid steel guns will likely bulge or burst, so don't sweat using a good Damascus barreled gun if you've done your homework.

Additional reassurance comes from the second phase destructive test in the Birmingham Proof House Trial. The barrels were subjected to increasingly loads until bursting, a bulge of .01�, or bore enlargement from .729� to .739�.
The following 5 barrels tied for first place in the second phase testing:
English Steel, Siemens - Martin process
Foreign Steel, Siemens - Martin process
English machine-forged 2 rod variegated Damascus
English �Superior Barrel Steel�
English machine-forged chequered 3 rod Damascus

The five barrels failed at 12.5 times the Definitive Proof load (which generated about 11,000 psi by modern transducers) or 11.34 Drams with 2.82 oz. shot (no attempt was made to estimate that pressure).
It should be noted that the 12th barrel (because of ties) Foreign Pointille� Twist failed at 5.77 times DP and the 13th (last) Foreign Four Rod Crolle� failed at 5.74 times DP.

Let's do the math on that one, 12.5 times 11,0000 psi (the standard proof load) is 137,500 psi before barrel failure (for both Damascus and early fluid-steel tubes). Talk about a safety margin! Admittedly, there are plenty of unaccounted-for variables here, but.....wow, what was I worrying about again?

Indeed Lloyd, but two points. The pressure increase was unlikely to have been linear. And these were specially bored 30" barrels without chambers and with wall thickness of .150" at 3", .092" at 6", .048" at 12" and MWT of .035 at 21".

Additional commentary found in Frederick Toms� Sporting Guns and Gunpowder, �Experiments On the Strength of Gunbarrels� regarding an additional study comparing brazed and unbrazed Steel and Damascus barrels:
http://books.google.com/books?id=inQCAAAAYAAJ&pg=PA14&lpg
These experiments serve to show what a very large margin of strength there is in a good gun barrel, when ordinary charges are used. The (Damascus) barrels which gave way earliest...had withstood the strains of�about four times as great as the regulation proof; while the steel barrels (Siemens-Martin and English �Superior Barrel Steel�) were tested...with charges averaging nearly five times as much as the ordinary proof-charge.
Although the steel barrels showed the greater amount of endurance, the strength of the Damascus was so much in excess of all ordinary requirements that no fear need be felt of their giving way when the work is properly done.

Dr. Drew:

I was perusing a box of Gamebore Traditional Game (made in Great Britain) 2 1/2-inch 20 gauge shells today (English 6s, fibre wad) and right on the side of the box it says "These cartridges are suitable for use in: Guns with a chamber length of 2 1/2 (65/67mm) or longer, nitro proofed to a service pressure of 3 tons/sq inch (850 kg/sq cm)". I sorely wish all cartridge makers would list this sort of information for the shells they produce, but no-matter. Is there a "reliable" conversion for tons/sq inch to tensile strength psi? Or....are there some other variables that need to be considered? Just plugging the numbers into an online converter gives me 6000 psi, which is comfortably below my ball-park figure of about an 8,000 psi limit for older guns. I might add that in a 6lb gun, these shells produced some fairly sharp recoil. Nothing terrible, mind you, but comparatively sharper than most of the RST shells I have used.

Gamebore is simply establishing that the shells are in compliance with CIP regulations, which do carry the force of law in the U.K.

The Commission Internationale Permanente pour l'Epreuve des Armes � Feu Portatives standards
http://www.cip-bobp.org/homologation/en/tdcc_public?page=1&cartridge_type_id=7
Both 65 and 70 mm 20g standard is SERVICE 830 BAR or 12,038 psi; Maximum SERVICE 950 BAR or 13,779 psi; PROOF 1040 BAR or 15,084 psi.
CIP pressures are measured by piezo transducers (not LUP)

One cannot know the pressure of those shells without a measurement.

Dr. Drew:

Appreciate that insight and, your point is a valid one. Nobody can really know the definitive pressure of any commercially produced shell w/o actually measuring each variant, but....for the purposes of general use, isn't it reasonable to assume that if a box of shells is listing a general service pressure designation, you can use it in similarly chambered weapons with some degree of confidence?

My primary complaint (admittedly minor) about how shotguns and shells have been (and still are) marketed, is the seemingly-constant shifting (evolution?) of how pressures are measured and then reported. There is a bewildering range of descriptions out there for both, and risk can only be managed if all the variables are competently understood.

Again, can I reasonably compare tons per square inch proof-marks (or in this case, CIP shell ratings) to PSI tensile-strength measurements in a way that allows me to judge what a "reasonable degree" of margin would be for safe use in an older gun? That, of course, assumes that the gun in question is "sound" (i.e., within it's originally designed parameters for use.)

I'm not asking for absolution here (although..that would be nice!), I just want to know if I'm on the right track.

"Can I reasonably compare tons per square inch proof-marks (or in this case, CIP shell ratings) to PSI tensile-strength measurements in a way that allows me to judge what a "reasonable degree" of margin would be for safe use in an older gun?"

NO. Too many variables Lloyd.
And this has nothing to do with whether the recoil of the load is appropriate for 100 year old wood.

What we know about pre-WWI guns and loads:
1. The gun makers said the guns were safe with the shells available in that period
2. Smokeless powder shells were in no way "low pressure".
20g 7/8 oz. 2 1/2 Dr. Eq. BULK Smokeless pressure was 8000-9000 psi; 7/8 oz. 2 1/2 Dr. Eq. DENSE Smokeless was about 11,000 psi.
3. We have a pretty good idea as to the wall thicknesses the makers chose.
4. The makers had a "safety margin". In the Birmingham Proof House Trial there was NO dimensional change in the 19th - 21st barrels, all Pattern Welded, until more than twice the Definitive Proof (DP) charge. As above, in the Second Phase trial, the 12th barrel (because of ties) Foreign Pointille� Twist failed at 5.77 times DP and the 13th (last) Foreign Four Rod Crolle� failed at 5.74 times DP.
5. My study, and one unpublished, showed NO evidence of the "because of low cycle fatigue, barrels get weaker over time" myth.
6. Fluid steel barrels DO have a bit less than twice the tensile strength of pattern welded.
7. Bad things happen to barrels over 100 years through misuse, inappropriate loads (steel), lack of cleaning, getting dropped, etc.
8. There is NO definitive NDT for pattern welded barrels (but I think we are getting much better at evaluating their integrity).

What do I think? How much of a margin of safety am I comfortable with assuming I will be shooting next to a grandchild?

I've just received an excellent condition, (60% CC, tight action, but with some case wear) Mid-Grade 16ga. Sears gun for barrel restoration. I've bumped this thread in order to find it easier for picture posting.

It has excellent HRF tubes, small scroll, with narrow ribbands similar to those found on Ithaca guns.

Lloyd, to add to what Dr. Drew told you:

I have several boxes of Gamebores marked the same as yours. Although the information on those boxes is valuable, it is also somewhat misleading. Mainly because it refers to two values (3 tons/sq inch and 850 kg/sq cm) as if they were equal--but they are not. The 3 tons is a reference to SERVICE pressure, while the 850 kg refers to PROOF pressure. And at the time those values could be found among the proofmarks on a British gun, both of them referred to pressures measured with lead crushers rather than piezo-electronic transducers, which means they cannot be directly converted into psi as we measure it today.

As Drew pointed out, however, the general thrust of the information is accurate. It's telling you that the shells in question are suitable for use in CIP "standard proof" shotguns. Drew gave you the equivalent psi values for service and proof pressure expressed in psi. Especially for service pressure, they are not that much different than our American SAAMI standards: CIP standard for 12ga service pressure is a maximum of 10,730 psi compared to our 11,500 psi. According to the former Birmingham proofmaster, referring to the 1954 rules of proof (the "tons" values): " . . . under the new rules of proof no arm will receive a more severe proof than hitherto." That means that any gun proofed since at least 1925--the proof rules in effect until changed in 1954--is good to go (assuming, of course, a gun in proof and in safe shooting condition) with any modern loads, such as your Gamebores, made for guns proofed under the 1925, 1954 or 1989 rules. The 1989 rules are the ones than required the metric terminology: 850 bar (or kg per sq cm). Guns proofed under the 1925 rules are relatively easy to spot because they will show both chamber length and shot charge: 2 1/2" and 1 1/8 oz, or 2 3/4" and 1 1/4 oz are the ones seen most often. Prior to 1925, shot charge was marked but chamber length was not.

Hope that helps clarify a fairly complicated subject. We and our cousins across the pond, as someone once wrote (G.B. Shaw?) are two peoples separated by a common language.