1951 probably,just as a guess. It's not drilled and tapped for 'scope mts which they started doing in the early to mid 50's depending on the model. They moved the receiver ring marking to the side when they started doing that.
IIRC #900,000 is right about 1955. That's about the ser# they lengthened the carrier spool to accomodate the 308,243,358 rounds.
Nice piece of wood! That'd run more than what you paid for the whole thing.
The cartridge counter is on '2' in the pic. Assuming the mag is empty, the rotor may need an extra 1/2 turn or more of it's spring to bring it up to full rotational power. If the rotor seems a little lazy or weak when you load rounds into it,,especially the first couple, it just needs to be re-adjusted.
Nice find,,should clean up to make a fine hunting rifle. I'd have bought that one just for the wood and parts.
Jacketed bullets often shoot fine is less than perfect bores.
I've had #436xxx that I just put the original sights back on for an old friend. 300Sav. cal. He hopes to take it white tail hunting later this month.
I have #714xx, also a 300Sav that I bought as a project. Nine extra scope and sight mount holes drilled and tapped into it's receiver !
Looks like a practice plate from a Black & Decker demo booth at Home Depot.
This ones from probably '54 (guess) and has the steel rotor instead of brass.
Slight patina,,Should clean up.