The burning characteristics of black powder used in early cartridges meant that these cartridges operated at low pressures, generally under 25,000 psi (~172,369 kPa). These cartridges were limited by their case capacity, and the only way to get more…
The burning characteristics of black powder used in early cartridges meant that these cartridges operated at low pressures, generally under 25,000 psi (~172,369 kPa). These cartridges were limited by their case capacity, and the only way to get more power was to increase the case to hold more powder BUT after smokeless powder was developed & had greater energy density , it was possible to generate far more power in the same small case at 8% - 40% higher than the standard pressure BUT below proof test loading of 2X 30% +P standard is designed so that if a shooter were to accidentally use a +P cartridge in a non-+P-rated firearm, the chance of a one-time explosive failure is minimal as long as the gun was in good physical condition.
firearms companies modeled toy cap & tape guns after
real muzzel loader gun percussion caps & maynerd tapes
saami Z299 3 & 4 Section 1 Characteristics of Primers & Pockets
centerfire pistol rifle primer & pocket Min & max dimension specification
shows small pistol & rifle primers are the same size,
BUT large pistol & rifle primers are NOT the same size, &
the smallest primer is the same size as the largest pocket
RIFLED SLUG GAUGE / BORE vs Max Diameter / caliber inch mm
10 Gauge .765 (19.43)
12 Gauge .735 (18.67)
16 Gauge .651 (16.54)
20 Gauge .606 (15.39
28 Gauge .535 (13.59)
.410 Bore .403 (10.24)
SAAMI: Sporting Arms & Ammunition Manufacturers’ Institute, Inc. pressures are often quoted in PSI gas pressure required to cause the case to expand & come in contact with the chamber & transfered to a conformal transducer indirectly
C.I.P.: Commission Internationale Permanente pour l'Epreuve des Armes à Feu Portatives french for "Permanent international commission for testing portable firearms" pressures are often quoted in megapascals & bars MAX 600 MPa (87,023 psi) measured INSIDE a drilled case
before this is was measured in copper or lead units compresses by the pressure
https://imgur.com/a/6rPUxGf
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