Not absolutely certain on this, but as I recall Nitro Proof became mandatory in Germany in 1912. The vast majority of pre 1912 German built guns were not Nitro Proofed as a quirk in the proof laws actually submitted them to undue pressures so most makers opted not to have it done. The few that did normally stipulated a very light service load for the benefit of proofing.
My understanding is that the then current proof laws required the same proportionate increase of the powder charge for Smokeless as it did for Black.
When you start increasing the charge weight pressures rise much faster with Smokeless than with Black.
