Two years ago I bought a NIB Nikon Monarch 4-16, BDC, Side focus. Had it on a 243 and it shot fine, held groups and adjusted perfectly. Just swapped it to a ruger No.1, 7 rem mag and problems started. Sighting in it started shooting Win 170 grainers (I think, not much sleep,but they are heavy). a At 25 yards it shot a 3/4 inch group. Took to 100 yards and first try was a 1 inch, 3 shot group. THEN - it shot a 4 inch 3 shot group. Then a 1 inch for 2 shots and threw a flyer 9 inches. Two more groups like that with barrel cooling down between groups and a 50 degree low humidity atmo situation. Thinking it might be me I let another shooter try. Rifle did the same for him?? Previously this rifle had a Leupold VXII 3-9 and shot consistent1 inch 100 yard groups with 150 grainers. I have heard of liking a certain load but not taking a disliking to it in the middle of a string! HELP! I leave in two weeks!