Has it been counterbored? Many overhauled Soviet arms have.
What he means by that is, if you look down the bore from the front (bolt out of the gun, please), do you see rifling right away, or is there a step inside the barrel before the rifling starts. Many rifles got worn near the muzzle end, so the response was to counterbore, or to drill a little ways down until there was solid rifling. It does not affect the accuracy and in some cases, will improve it from before. It is not a dangerous thing and your gun will be safe to shoot.
Welcome to the world of Mosin-Nagant. Although this is a great forum, you might also want to check out www.surplusrifleforum.com
, which is a forum strictly for surplus military guns, and they have years worth of M-N info there.
The Doc is out now.