Bought some Hornady GMX bullets to test in my rifle. 165gr GMX is longer than a 200gr Sierra gameking so I thought they might just work. I loaded 3 different loads. 2760 fps, 2850fps and just over 2900fps.
About 2.5mm (0.1 inch) from the lands. All 3 loads printed less than 1 inch at 100 meters with the fastest one the best at about half an inch.
So now I just have to go and field test them!