what is a reasonable expectation for 5 shot groups at 500-600 yards with this setup. winchester model 70,26 in. shilen select match 1-8 inch twist,8.5x25x50mm leupold shooting 139 gr.lapua with lapua brass.the gun weighs about 13#s, and shoots 1/2 inch down to 1/4 inch groups at 100 yards.I've never shot long range before and would like an idea on what I can reasonably expect. thanks timbo