Wondering ?????

[Drew Hause]

Craig: Austria is a member of The Commission Internationale Permanente pour l'Epreuve des Armes à Feu Portatives
http://www.cip-bobp.org/homologation...idge_type_id=7
12g 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.
SERVICE pressure 740 BAR = 10,733 psi;
Maximum statistical individual pressure 850 BAR = 12,328 psi
PROOF 930 BAR = 13,489 psi

12g 76 mm = 3” LEAD “High performance/superior proof” transducer pressure
Service 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;
Maximum SERVICE 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;
Maximum SERVICE 950 BAR or 13,779 psi;
PROOF 1040 BAR or 15,084 psi.

[C.O.B.]

I spoke to Steve last night and the barrels and chambers were to the original specs regarding wall thickness and chamber length. These barrels were not honed in any way. The bulge is approximately at 2 3/4 inches and the chambers are 2 1/2. This probably occurred by using a high pressure 2 3/4 inch shell in a gun chambered for 2 1/2 inch shells.

As a note of possible interest a friend of mine was shooting his Fox Sterlingworth when the barrel burst at the chamber. The previous shot went off without any problems and the target was broken. Sometimes things just break.

[Drew Hause]

Thank you Rich. Could you please inquire as to what the wall thickness at the end of the chambers, at the forcing cones, and at the point of the bulges measures? That information is quite important to those of us who chose to use Pattern Welded barrels, and have followed this thread with great interest.

Does The Parker Pages have a Mechanical Specification Drawing with the "original specs" for wall thickness by gauge?

[Sheepherder]

Has anyone thought of the possibility of shells loaded (or re-loaded) with STEEL shot? Both barrels, with the same problem, at or about the same time? It's got to be a load/barrel relationship issue. Not an obstruction.

[OH Osthaus]

Originally Posted by Hal Sheets

Has anyone thought of the possibility of shells loaded (or re-loaded) with STEEL shot? Both barrels, with the same problem, at or about the same time? It's got to be a load/barrel relationship issue. Not an obstruction.

In that case -I believe the ring bulge would be at the chokes. Not the forcing cone

[John Taddeo]

Gotta ask.... on the pressure graph illustration, is the peak pressure generated (as shown at 1 inch from the breach) from the end of the shell at the forcing cone or in the base of the hull ??

[Drew Hause]

John: short version is that pressure was measured by lead crushers placed in holes bored in a special barrel every inch. Pressure is essentially in all directions. "Chamber Pressure" is usually the 1" from the breech.

The top chart is TONS/sq. inch and is for 1 1/4 oz 3 3/4 Dr. Eq. loads
Ballistite maximum pressure at 1” was 4.9 Long Tons = 15,344 psi
Schultze at 1 3/4” was 4.5 Long Tons = 14,000 psi
DuPont Bulk at 1 2/3” was 4.1 Long Tons = 12,656 psi
All three beyond today's SAAMI recommended max. pressure, and turn-of-the-century Live Bird competitors were using those loads in damascus barrel guns.

Better numbers from another pressure - distance graph
Ballistite Dense (1 1/8 oz. at 1232 fps = 3 Dram Equiv.)
Breech - 2.9 Tons per Square Inch (UK, Long) = 8624 psi
(Using Burrard's conversion formula: 2.9 x 1.5 = 4.35, 4.35 - .5 = 3.85 TSI, 3.85 x 2240 = 8624 psi)
2 1/2" - 2.2 Tons = 6272 psi
6” - 1.2 Tons = 3718 psi
12” - .81 Tons = 1602 psi

3 Dr. Schultze Bulk 1 1/8 oz. at 1220
Breech - 1.69 Tons = 4558 psi
2 1/2” - 1.49 Tons = 3886 psi
6” - 1.36 Tons = 3450 psi
12” - .92 Tons = 1971 psi


Wallace H. Coxe, in “Smokeless Shotgun Powders: Their Development, Composition and Ballistic Characteristics” published by E.I. du Pont de Nemours & Co., 1927, “Measurement of Pressures”
The common method of taking pressures in small arms in this country is known as the Radial Pressure system. A housing is built around the barrel, and a hole drilled through the housing and barrel into the chamber at a distance of 1 inch from the breech and at right angles to the axis of the bore. The hole is then bushed and drilled to a uniform diameter of 0.2250 inch. Then a piston is made the length of the piston hole and 0.2250 inch in diameter. Next the piston hole is lapped to permit the piston to fit snugly without either sticking or getting out of alignment.
In firing the gauge, the piston is inserted and seated, then a lead crusher cylinder is placed on the head of the piston and held firmly in place by a screw and anvil attachment built into the housing. When the cartridge is fired, a portion of the same gas pressure that pushes the bullet through the barrel drives the piston against the lead cylinder and compresses it.
The length of the lead crusher cylinder after compression is naturally less than before the shot was fired and the difference between the original length and the length after compression therefore represents the amount of pressure which has acted upon the lead. Thee exact pressure is read from a table giving a pressure reading for every remaining length reading and commonly called a Tarage Table.
Pressures that are determined at ballistic laboratories are merely relative values and are not absolute values.


NOTE: The Tarage Table conversion may be for pressure expressed as Tons / Sq. Inch or Pounds/ Sq. Inch (PSI).

Rifle pressures were usually measured by copper crushers (CUP).

Pressure is now measured using piezoelectric transducers.

[Fishtail]

Well.....I guess that settles the question of who the guilty party is once and for all. If I were in his shoes, I wouldn't go around advertising what I had done....or at least I would accept responsibility for it.

[Bill Murphy]

Drew has a good request, but there is some stretching when a barrel bulges or ruptures and you have to be careful where you take your measurements.

[C.O.B.]

I'll try to get the measurements requested. Steve is in Montana currently.