Was all the ammo from the same lot? My Ruger was shooting cloverleaf groups with a certain lot and 1.5" groups with another lot. I switched to a different brand and went back to 1/2" groups. Now I have to go back and check each lot until I segregate the "good" and "bad" lots. We shot 5 brands/bullet types through Son's Ruger and got groups from 1/2" to 2"-same rifle and distance.
BTW your reference to the drop of the 17HMR @200 yards compared to 308 is incorrect.
My info indicates all 17HMR ammo is made in the same plant(even Winchester).