The range is south of Houston, TX, pretty much flat as it gets. You have to shoot past the 100 yard berm to get to the 200 yard line. The wind was blowing into the back of the 100 yard berm directly toward the bench. I don't have wihd flags but would guess that there were big eddy's coming off the 100 yard berm into the 200 yard line of fire.
I was surprised Saturday to see that I was hitting higher at 200 than at 100, still getting nice groups though ....
I'd figure your're getting lift when the wind hits the back of the berm and shoots up. That would be pretty much like shooting across a canyon up here, you'll get a thermal somewhere between you and the target and shoot way, way high.
I've watched hawks grab one of those thermals and gain altitude much faster than a fella would expect.
I would guess something quite different...what are you using as a rear rest (and front rest for that matter) ...inconsistent rear rest technique/ poor selection of rear rest 'material' could change MPI from one occasion to the next....you'll still be able to shoot great groups; they just won't be in the same place each time...which could lead to apparently 'odd' ballistics if your rest/technique causes different vertical movement of the rifle in recoil from occasion to occasion..haven't explained this well -in a rush- hope it makes some sense!......I learnt almost same thing the hard way! [img]/ubbthreads/images/graemlins/smile.gif[/img] Could never work out what was going on ballistically and was blaming my scope until a friend (far more experienced than me)told me to change my field expedient rear rest...problem solved. Hope this may be of help.
Went to the range again yesterday, no wind this time. Also 65 degrees, YAY! To answer Brown Dog's question, I have been shooting off a Harris bipod with a normal benchrest rear rest.
So with no wind I get 1.5 inches high at 100 and 1.28 inches high at 200 yards. Works out on the ballistic program if velocity is 3500 fps and the zero is at 245 yards. I did chrony them and and got an average of just over 3450 fps. (Also shot my first 1/2 inch 3 shot group at 200 yards.)