I totally agree. This issue was canvassed in some threads earlier this year (see Doubles ), but I would say that the pressure curve is more important than peak pressure.

There is some confusion about what is was being measured in the British Proofhouse pressure measurements. Leaving aside the issue of translating "tons per square inch" into modern transducer measurements, and the inherent limitations of the procedure, it was effectively a measurement of the pressure that the barrel, rearward of that point where the projectile had travelled to at the time that the pressure peak was reached. This coincides with that part of the barrel where the wall thickness is greatest, and where there is perhaps the greatest margins of strength.

It said nothing about the pressure levels that the barrel is subjected to as the projectile travels further down the barrel. The pressure curve will reveal something of this, but there is no way of knowing exactly what pressure each section of the barrel is subjected to, since the projectile will accelerate down the barrel at different rates due to a number of factors (powder burning rate, projectile weight, jacket and core construction / hardness, etc).

To illustrate this, consider the hypothetical situation of two loads with different bullet weights optimised through carefull reloading to produce the same peak pressure and pressure curve. Yet the lighter bullet will have a shorter barrel time and higher muzzle velocity. This means that the thinner sections of the barrel at the muzzle end will be subjected to higher pressures than the load with the heavier bullet, simply because the lighter pill will get to the muzzle quicker. This seems counter-intuitive, and it could be argued that such loads would be difficult to achieve in practice....but?

The problem is, nobody really knows what the safety margins are, since the original British proof system tells us nothing about that. So long as the pressure curve for a Nitro powder reload shows pressures below what is obtained on a modern Black powder load that approximates original ballistics, then that has got to be a reasonable starting point.

Sherman Bell, et al, have have at least bothered to to some homework to back up the notion that Nitro-for-Black loads can be gentler on vintage double rifles, rather than simply spouting the tiresome mantra about the perils of using Nitro powders in Rifles (and Guns) carrying Black Powder proof.

About at vacuous as the old furphy not shooting Nitro cartridges in Damascus barrelled shotguns, even if they are Nitro proved.