Strength of the components / barrel / bolt is what I was referring to. A 6x45 AR using 5.56 brass should be just as safe @ 62k psi as a 5.56 AR using 5.56 brass @ 62k psi.

The root of my curiousity came from studying 5.56 load data with max avg pressures around 60k vs. 6x45 data with max avg pressures around 50k. My assumption was 6x45 data was built around acceptable pressure for its"parent" case - .223 rather than its "step parent" case 5.56.