That sounds to me pretty much what I first experienced when I first ditched the crappy scope from the Rem 783 .223 Rem I bought and slapped on that first Vortex Crossfire II 2-7x32mm.
You'd be shooting from the bench, and they'd seem to stay grouped...ish... then... from one shot to the next.. for me.... it seemed as if it flipped over across a Y-axis running thru the center of the bullseye. You'd shoot a for more and then WTH? It'd move yet again, but then still do a couple more shots at that new location.
In my instance... one of the Allen Screws, unbeknownst to me, had managed to have it's threads strip ever so slightly.
So it was luck of the shot wether or not it caused a slight amount of shifting of the scopes positioning within the rings due to that one stripped screw. And we're talking extemely small shifts that you wouldn't be able to visually see or detect. But extrapolate those shifts out to 100yds and such and they become very apparent.
That was the first time I ordered a DNZ Game Reaper 1-piece mount... which instantly solved that problem... and now? After an incident where I had a slip-and-fall that shattered my wrist, with the rifle in my hands at the time of the fall... where the scope itself had it's lip on the objective end actually even become bent!.. and it was STILL ZEROED!!! So their mounts are nice and solid!
I always slap on those DNZ Game Reaper 1-piece mounts now because of that incident.
