Hi Mark,
The Caliber should be stamped on the Bolt Carrier in the 2pm position (right side of firearm) when the bolt is in battery. I have also seen the caliber stamped on the top of barrel over the chamber (but only for 300 Savage Caliber versions).
If it's made before early 1930's it should a Model 8, and after that it should be a model 81. The usual visual clue is the Model 8's had a straight stock, whereas the Model 81's had usually a semi pistol grip.
Also the factory Caliber's were .25 Rem; .30 Rem; .32 Rem and .35 Rem and finally 300 Savage..........having said all that, it could be the case that the caliber is not marked (even thought it should be), which might be an indication of a Gunsmith altering/repairing the rifle in the past, and not marking the caliber (not unheard off). With no caliber marking, if it were me/my gun I would do a chamber casting (Brownell's will have casting material), and verify via a reloading manual, and also slug the bore with a lead ball to determine lands and grove diameter (easy, cheap, lots of video's on youtube on how to chamber cast and slug a bore)
These were very well made guns, and if maintained even reasonable well, it should last another 100 years.
I would recommend an exam off the bore with a good light for signs of more than acceptable frosting/rusting in bore, but if at first glance the bore looks rough, I have found that sometimes after a really thorough cleaning underneath the crud was a very fine bore indeed.
Enjoy the Gun, the .35 Rem and 300 Savage are factory ammo to this day, the other calibers you may have to reload for, and I would NOT recommend using handloads from someone else...too many horror stories and its now more that 15 years since someone blew up a M1A beside me (magazine floor plate hit my left shoulder) at Andover Sportsmans Club with someone else's reloads. So its not just something you see on youtube.
Best, Seamus
