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.
08-16-2016, 06:59 PM
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