Any Idea As To How Old These Are?

[Bruce Day]

Max load is SAAMI maximum for the gauge and chamber length. You'd have to go to the SAAMI specifications to find it, its probably around 11,500psi, but that's just my memory. Its not proof, its the maximum service load, which is a theoretical limit determined by proof minus 20%. And to be clear, proof is not rupture either, typically one can double proof before rupture.

[Bill Murphy]

That box is a 3 3/4 dram equivalent load which was advertised at 1330 fps.