I've been shooting several rifles lately, and my groups with one of them has little horizontal dispersion significantly more vertical dispersion. My groups are 2-3 times as high as they are wide.
I've checked to make sure the action screws are tight, although I haven't torqued them. Same goes for the scope, which also seems to hold zero just fine.
I'm chronographing everything, and my velocity numbers are pretty good. (ES 30fps, SD less than 10fps, MV about 3000fps) Besides, so far I've only been shooting at 100 yards so anything but major changes in velocity wouldn't show up.
I'm shooting off of a lead sled, not offhand. I guess it could still be the "jerk behind the trigger", I make no claims of being an extraordinary rifle shot, but my groups with other rifles show no vertical stringing.
What else might be the cause of vertical stringing? And what about the cure? Would a bedding job help?