The lack of a shoulder concerns me also - but that is merely an opinion and that problem can be overcome.

I would not be too hasty in accepting that CH4D made the dies the correct size to start with.

A fired case, when using a good strong load, will give a better indicator of what the chamber actually looks like. Add .001" to a case dimension for chamber size - IF that strong load has been used, otherwise that number is of little use. Of course a chamber cast, measured at the correct time, will also give the proper measurements.

.456" on a fired case indicates an actual .457" or .458" shoulder in the chamber - perhaps - IF it was a stiff load generating some 50,000psi or more was used, then measured after firing. If the pressure was lower than that and the case was well annealed perhaps that measurement is still useful. If the case was not annealed, the measurement is not to be trusted.

Due to the heavy pin fall of a Mauser and the strong chambering power of the action, I'd make sure all my bullets engraved in the lands when chambering - of course one must start low with their data and build loads that are safe in THAT rifle, when Loaded in that manner.

That is how we load small bore ammo - ie: the .17's & .20 calibre bullets are seated to engrave in the lands when chambered and the data for that seating depth is started low, then developed at that seating depth, there are NO pressure surprises and the ammo is perfectly safe. The reason it is loaded that way is that they usually deliver the best accuracy when seated to engrave the lands - in straight chambers, that is.

NEVER start with a maximum load, of course- we all know and adhere to that, don't we?

I'd be happy with that load, as well, Cordite. Nice rifle!!