Looking at this target I would say wind drift opened up your group, but I believe you need to add a little powder to your load. This will take care of the up and down stringing. Add powder to your load until you get a clover leaf group. Then you have found the correct amount. Too much powder will string left and right. An old bench rest shooter taught me this and although at first I didn't belive it, it really is true. I work up loads like this all the time and after I do get the cloverleaf, I know that unless I change something else like case, or primer, this will be the best load for that particular powder. Only after I have made those changes will I try another powder and start all over again. Other than that, I have to agree with the other members. Scope paralax can cause shifts in groups, as well as bullet selection. Some bullets "go to sleep" better than others at long ranges. Use flags to indicate wind shifts, and shoot at dots. Remember...aim small, miss small.
