One other thought, don't take this the wrong way - the gun is cock on closing, have you ever operated one before? Push it forward, then push it all the way forward until the cocking piece extends, then down. It is a different feel that takes a bit of getting used to, some shooters hate it, I prefer it with a properly designed bolt (the P14/M1917 comes to mind). It should be smooth though. Alternatively, as said above could be grease, crap in the chamber... I assume this is happening when dry/unloaded correct?