While the design of the Model 99 action didn't change dramatically until the tang safety style mostly superseded the lever safety style in 1961, the metallurgy and heat treatment did. At some point in time, I'm sure Calhoun knows the details, Savage would require actions to be re-heat treated if they were sent to the factory to be rebarreled.
Savage varied on their opinion on early 99 heat treatment over the years. Some years it was guns made prior to 1928, later it was ANY conversion to 250 or 300. The factory demanded on redoing the heat treating if converting the 99 from something like 303 Savage or 30-30 to 250-3000 or 300 Savage.
They wouldn't touch receivers under serial number 90,000 for converting to 250 or 300.. in fact the factory wouldn't work on them at all, really.
And you can't convert any Savage 99 under 900,000 to a 243/308/358/etc, the internals and magazine won't work for the longer cartridges. It'd be a single shot. I don't know of any change to heat treating starting at serial number 900,000 in 1954 for the 243/308/358 guns. They just had to reconfigure the internals to allow the cartridges to fit.
All that aside.. I have too many guns in 250 Savage to want to load some rounds hot for my couple of bolt actions and risk shooting them in a 99. I hate stuck bolts and brass.. But as long as it's a sane load and not hotrodding it like crazy, I can understand wanting a bit more oomph out of it for a modern bolt action.
