what type of ammo are you using? some rifles have tight chambers and the bulgarian surplus ammo does not do well in some of them. as stated you may also still have some dried cosmoline in your chamber. when I bought my mosins I threw them both in the bath tub with the hottest water that my heater could muster, after about 5 minutes in there I ran dry patches down the barrel and used a 45 cal brush on the chamber, I don't have that problem with either of mine.
also I hate to break it to you but there is no paper trail for mosin nagants so there is no way of knowing which rifles were issued and which ones weren't. many of these rifles were crude at best but they are robust enough that it doesn't really matter if they were issued or not. they pretty much all age the same.
What type of Nagant was it? If they were selling M91/30s for $135 that's a bit overpriced, but if it was a M44 then you got a good price.
actually $135-150 is about average. there were 3 91/30s at the last gun show I went to, they were all priced at $190+ the age of $80 mosins is well and truly over, I'm sorry to say.