Ran into a tidbit in the "Complete Guide To Handloading" by Philip B. Sharpe, copyright 1937. Underline is mine.
Found it interesting since there's no mention of heat treatment. Just the design of the bolt.
Savage guns also are built to stand heavier pressures than normal. However, in 1933 a friend of the author acquired a model 1899 - 30/30 with a poor barrel and wrote Savage for a quotation on the fitting of a 250/3000 barrel to his action. The factory wrote him: "We do not care to subject some of our - 30/30 receivers of early production to the increased breech pressure of - 250/3000 cartridges, and for this reason we have constantly declined to convert rifles in this manner... This is more a matter of policy than anything else. The present Model 1899 Savage rifles are being used with cartridges developing breech pressures of from 45,000 to 48,000 pounds per square inch.. All barrels are proof tested with a pressure load in excess of 55,000 pounds. in 1908, however, there was a change in the design of this model which is not generally known. At serial number 90,000 the original square-should locking lug at the rear end of the breech was changed to the present oval design, which gave a much better distribution of the pressure."
