As far as your original question, you cannot date a mosin by its serial number. Many believe the numbers were just put there in order to make certain that all the tolerances were within spec as the rifle was assembled originally. After that, it was just to keep track of parts in a relative fashion. To date it you must follow the stamped year. The year stamp on the receiver is almost always followed by the "n" looking symbol. This symbol stand for "God" and also means "year". As far as the "c" symbol it is a special designation for the barrel "quality" and really doesnt mean much. There is no record for what the barrel quality designations actually meant, whether for accuracy, or type of metal, ect.
If your rifle has a star shape stamped on the receiver it was manufactured in the Ischvek arsenal and if it has a triangle with an arrow inside of it, it was manufactured in the Tula arsenal.
On many of the re-arsenaled Mosins, the original year is completely stricken through and the new year is stamped in place of it. On most of the Tula re-arsenaled firearms the original year stamp is left un-molested and a "/" is placed after it with only the last two numbers of the year stamped. It would look like this "1942r/53" for example, this would mean original manufacture was in 1942 with a re-arsenal in 1953. the little "r" or "n" is the symbol meaning "year" (technical translation is "year of our God" ie-A.D.).
Well i hope that that this helps you a little. Goodluck.
On a side note- If you ever wish to help that Mosin out and get a bit tighter groups I strongly suggest this sight. The one thing he misses out on is how strongly corking your barrel helps. I will also post a link for that as well. After floating my barrel and corking it i am achieving 1 1/16 inch 5 round groups at 100 yards. Im extremly happy with that. Seeing as how i bought the rifle for $89.00.Good luck.
Guns and My Other Hobbies: Accurizing the Mosin Nagant
and for corking--http://www.theboxotruth.com/docs/edu63.htm
info for general accurizing--http://www.surplusrifleforum.com/viewtopic.php?t=529
Glass bedding and lots of info--http://1-800-magic.blogspot.com/2010/08/how-to-make-sniper-rifle-part-5.html