Remington says that it translates to SAAMI's standard max operating pressure for the .45/70 of 28,000 PSI, and they're probably technically correct. Their web site says of the .45/70 SPR22 "For use with SAAMI compliant loads only (28,000PSI operating pressure)". Yeah, no Garrett, Buffalo Bore, etc....I have no idea what HST means. The markings on the barrel indicate that the gun is proved to the current CIP standard pressure for the .45/70, which is 2,200BAR/31,900PSI (14.50375 PSI = 1 BAR).

Before someone makes the jump, the difference probably isn't lawyer padding, nor does it mean that this gun is proved to a higher pressure standard than what Remington is stipulating. CIP PSI and SAAMI PSI are not the same unit of pressure, nor are they convertible. Both standards represent chamber pressures measured by piezo electric transducer, but the equipment and methodologies - and the resulting measurements - are not the same. CIP uses a drilled case, SAAMI doesn't, and transducer placement protocol also differs. That's why CIP MAP is often (but not always) higher than SAAMI's for a given rifle cartridge. In other words, the two standards are almost certainly much closer together than the values suggest - and standard SAAMI is essentially what the rifle is proved for. You can bet that Remington understands this perfectly, hence the warning on their web site.