what choke are you using?
too tight a choke can constrict things as they leave the barrel and cause erratic patterns, this is why most ammo company's recommend for slugs and buck shot to be in a cylinder/improved cylinder choke, so not to effect them as they leave the bore!( or a rifled choke for slugs)
and NO at 30 yards wind shouldn't effect buck shot, unless its like hurricane winds LOL

Point of aim also will change when you go to different loads, so, every time you switch you may have to fine tune to new round of choice, and this can vary from brand to brand on same size shot in shell!