Hey, there's no such thing as a stupid question unless its asked by "yours truly." Marlin upgraded the steel in their barrels in the late-1800s/early-1900s for use with then new smokeless powder loads. They sold the old barrels until they were used up with the caveat that they were to be used with black powder loads. The upgraded barrels of that period are marked "smokeless steel." I never heard of any sort of transition period barrels with Savage, though the older receivers are not recommended for use with modern high power cartridges such as the 308 series of rounds. I don't know when the metallurgy of the 99 made the improvement but I'm sure there are those on this forum who do.
Marlin I have serial # dates to 1904 as best I can tell. The first number is hard to tell if it is a 3 (1904) or an 8, dates unknown. Best I can tell with a magnifying glass is a 3.
only markings on the barrel are, 25-20 M next to the receiver, Marlin Fire-Arms Co. New Haven CT. and the pat.d dates. Tang stamped Marlin 94.
Nothing about the steel.
I would think a 1904 firearm would have been made for smokeless powder.
