Thanks Dave.

Interesting claim that the 20g load "breech pressure is maintained at a low point" despite "the velocity exceeds that of the present maximum loads..."

The DuPont Ballistic Table published in Parker Brothers' The Small Bore Shotgun c. 1920
http://parkerguns.org/pages/PDF%20Documents/Small%20Bore%20Shotgun.pdf
16 gauge
2 3/4 Dr. Eq. 7/8 oz. = 7,035 psi
3 Dr. Eq. 1 oz. = 8,980 psi
20 gauge
2 1/2 Dr. Eq. 7/8 oz. = 12,655 psi
+ 10-14%
DENSE Smokeless Powder pressures would be 1000 - 1,500 psi higher

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