Rough 66
As others have said, its not the smoothest of actions at the best of times, the only thing than can sound like grinding that is not an indication of a more serious problem is the big screw adjustment under the front of the fore end which tensions the cocking link.
If its too tight, or got dry, it can scuff up the underside of the link upon which it bears, just drop the action out of the stock, make sure there are no scuffs on the bearing surface of the link or the screw, clean up, grease, and reassemble. There is probably a measurement some where but I always did the tightness by feel, just enough to hold the link in smoothly and not let it "crack" over centre, but not too tight to bind up or scuff.
If its not that contact a rebuild expert, a little fiddling if you don't know what you are doing can cause a lot of damage with one of those! I would suggest and recommend "Wonky Donkey" on here.
Best of Luck
Robin
Walther KK500 Alutec expert special - Barnard .223 "wilde" in a Walther KK500 Alutec stock, mmm...tasty!! - Keppeler 6 mmBR with Walther grip and wood! I may be a Walther-phile?