good get; m38's are starting to dry up. should have at least 3 serial numbers on them; receiver bridge, bolt, bottom of magwell. See if it is counter bored, look down the muzzle, to see if it looks smooth for about an inch, and then rifleing starts. if no counter bored, then possible it is unfired.
No worries, the m38 is a great all around rifle; lots of bullets out there; new and milsurp. just clean with hot water, after you fire milsurp, you can use window cleaner as well, but hot water cuts salts as well as anything.
to me, I like the rifles better than most 308 stuff out there; it can take a beatdown, it fires a hot round, they come from 147 grain, all the way up to about 205 grainers, the sweet spot for heat, speed, and accuracy should be between 170 and 180 grains.
I like the 185's from brown bear, in hollow points; very nice accuracy.
Also, if you get a chance, fire it at night a few times, and take some video; they are total flame throwers.
Everything you wanted to know about mosins are on 2 sites;
check there for your trigger job, and to cut Sticky Bolt Syndrome, which may
or may not effect you;
http://www.surplusrifle.com/russianmosin189130/index.asp
http://7.62x54r.net/
oh yeah, did you get the green dog collar sling, with the leather straps
on the ends? Cuz' if not, then that alone is the best completeing detail of the
mosin. They can be had for about 20 bucks, and they are mostly brannew.
