I would first check to see if scope mount or bases might have worked loose, happened to me a time or two with the results you described. I have had a new scope malfunction due to excessive recoil, although this is probably not the case with your rifle/scope combination. I have had several Tasco scopes over the years with only one crosshair breakage. Third possibility "the flinch factor" A young lad came over last weekend with a .270 and shot well first 5 rounds, then groups spread dramatically due to flinching, the more he shot, the worse it got.