Inspect the bolt for an electro pen numbered marking, it should correspond to the receiver serial number. Cycle the bolt (obviously ensuring it's not loaded first). Try the trigger, being sure there is some additional trigger travel after the sear releases. The bolt should cycle without any binding.
Because there's bound (good word, 'bound') to be a Cosmoline buildup, not much else can usually be derived, and bright bores seldom exist on Mosin-Nagants due to their corrosive nature of their ammo. Many are also counterbored at the muzzle end to make up for cleaning rod wear. Neither of these conditions are especially bad but one should not have high expectations about arsenal refurbished rifles that then ended up cradled lovingly by Russian armorers in storage for well over a half century.
Once the
Cosmoline is fully cleaned out (if you think it was easy, you didn't get it all), surplus spamcan ammo shooting to 2MOA or better indicates you have a (relatively) 'good' one.
Before you despair, remember that illiterate Russian farm boy conscripts used them to kick the Germans off their real estate and chase them all the way back to Berlin. 'Quantity" is also a valuable quality.
If you want to learn more about what's in certain cleaners, lubes, etc., and maybe take crack at making up some such, see Fr. Frog's
site. I like a combo made of K1 Kerosene, Acetone, Mineral spirits, Marvel Mystery Oil, Murphy's Oil Soap, and some 10% Janitorial Strength Ammonia. Combine the Ammonia and Murphy's, then add the others; shake well. Keep well away from children and stupid people. Proportions? Still working that out. I follow up with Windex, dry patching, and then some bore oil, and this is also what I use for corrosive ammo/black powder bore cleaning. For the Russian Spamcan ammo, I start out with Windex and keep spraying/patching out until the patches start turning from black to grey, them use more conventional cleaners, saves a lot of time at the beginning. FYI, I don't use bore brushes.
I think 91/30's are like popcorn; I have three, and I wouldn't mind having another...
Greg