I'll be going I've fixed a few mosins for my friends etc.
Most don't clean the Cosmo out of the chamber area good enough and that why they get sticky bolt. That or the pocket the rim sits in has been peened in.
A easy way to tell if that's the case is this .
Take the bolt out , try to click the rim into the bolt face .
If it's a bitch etc tap the little lip out just a hair .