It is not normal to need to tighten the stock bolt every 3000 rounds. My first guess is that you are not tightening the bolt tight enough. You don't want to over-tighten as that is what tends to cause cracks though the wrist of the stock. Under-tightening can also lead to cracks.
Tighten the stock as you normally do, and then give the wrench an extra 1/16 of rotation and see how long it stays tight. if it still loosens, give it another 1/16 turn.
Thank's guys, I'll check the washer and tighten it a little more. Didn't want to tighten it TOO much as I've been afraid I might crack the stock? Yes, it was a NEW 687 combo when I got it from Etchen a few years ago.
When I moved from Michigan to Arizona, the wood on all of my guns shrunk. Literally every stock became loose eventually and gaps of .004" where before there were none became evident on the fore end where the wood meets the iron.
One year later, things have stabilized. But here's a little trick...wrap the stock bolt threads with a little plumbers tape (opposite direction of the threads) and you won't have this problem.