Exactly the point. You can't mix data from different bullet types and expect the same limits. The start pressures are too different.
The same caution would apply to a all copper Barnes versus and jacketed or lead bullet. The all copper bullets are very long compared to their same-weight jacketed or lead bullets.
Not just longer but the start pressure is about twice as high unless it is a design with little bands at the bearing surface, in which case the difference is around 1½ times as high. The Lehigh Defense 9mm bullets are monolithics that don't have that. In either case, it takes more effort to get them through the throat and engraved by the rifling because they are harder. That means pressure gets higher and powder burns faster before expansion starts, raising peak pressure. The BHN is somewhere around 80 (based on Matweb's ¼-hard gilding metal number). With Berry's and the now-defunct Ranier plated bullets it is the other way around. The copper plating is a good deal softer than jacket gilding metal both because of the alloy difference and because it gets none of the work-hardening that drawing and forming a jacket does. I note Hartmut Broemel's experiments lead him to put plated bullet start pressure the same as cast lead, which is less than half his jacketed bullet numbers for handgun rounds. However, I don't see an allowance difference for thick plated verses thin. It would be fun to make some measurements of that.
