Clean the chamber with acetone, or acetone based nail polish remover.
Some european milspec pistol ammo originally intended for SMG use has coated cases and/or thick neck sealants that can end up coating the chamber with a laquer like gunk. When the gunk is warm it grips the case, when cool it lets go.
I've seen this problem with some 7.62X25 ammo.
Some propellents can foul a chamber in the same way, though the surface of the chamber would look bright and shiny. The chamber pressure irons the fouling into the surface and the case moving against it during extraction polishes the surface.
As the crust gets thicker it can prevent the case neck from releasing the bullet as easily as it should, greatly raising chamber pressure.
Anyway, always clean the begeezus out of any firearm before you consider any alteration to springs or polishing of chambers.