Jones, I have no exact dates at hand right now, but I'm sure you'll find that ballisticians and proof houses had pretty accurate means of measuring peak pressures before smokeless powder came into common use. In fact, they were measuring pressures at various points along the length of gun barrels, and plotting pressure curves. This information helped gunmakers design and build barrels with adequate wall thickness to withstand firing without failure, and with a built in safety margin without excess weight..
Even so, cartridges weren't loaded to a 'service pressure'. They acheived this only indirectly and the guns were designed to withstand the pressure from the commonly used loads.
