Flash,
Now days all the manufacturers of shells and your reloading manuals for shotshells go by PSI. The following is a list of maximum allowed pressures for the various gauges.
SAAMI Shotgun Pressure Specifications (Maximum Average Pressure in PSI)
(All Piezo measurements unless specified)
Cartridge Maximum Average Pressure
10 gauge 11,000 (all)
12 gauge 11,5000 (all but 3 1/2" mag)
12 gauge 3 1/2" mag 14,000
16 gauge 11,500 (all)
20 gauge 12,000 (all)
28 gauge 12,500 (all)
.410 bore 2 1/2" 12,500
.410 bore 3" 13,500