Thanks Maraki,
My Jeffery is proof marked exactly as the one you examined was, 42 Max with 300 grain bullet. However, from my understanding the proof load was not the load the rifle was regulated for in the case of most 333 doubles. The barrels of my rifle are engraved with "250 grain bullet." This makes it harder to extrapolate a load using the proof marks on the rifle as a starting point. A quandry, for there seems to be absolutely no reloading data for this cartridge, which in fact was a popular cartridge. Any help anyone? There are a lot of 333 doubles out there somewhere. Look on this as a challenge. Thanks, Keith