Chips and cracks are caused usually by the movement of the metal against the wood. As a stockmaker, it is poor workmanship to leave gaps around the metalwork on a sidelock. One can make the fit close enough that the locks don't bind on the wood.
After much recoil/wood compression the fit becomes too tight. It may take a long time or a short time depending on the way the stocker inletted the action into the wood and the wood pore structure itself.
Your question about how to stop it is not an easy one. If the wood compression is sever, one must stop the compression. Epoxy can and has been used to stop this process. Of course there must not be any oil in the inletting in order for the glue to adhere to the wood. You fix the cracks at this time too.
Sometimes the easy fix is to just releave the stress areas. Scapers, knives, chisels, or sandpaper have been used to accomplish this action. In my opinion though, this is not a solution to the problem. It is is only a bandaid. In my experience cracks and chips are a symptom of the problem that must be addressed not the cause. Ok, poor inletting doesn't help either.
