Thin barrels on light rifles do require different methods of shooting for groups. As some have stated, wait between 3 shot strings; I wait 15 minutes ... what is the rush to sight in and do it right? This is not convenient, but it is even less convenient to carry a heavy rifle if you are hunting the mountains of Colorado ... trust me!
If you shoot anything like Elk or Moose, choosing one bullet weight is a good thing. It is better to shoot heavy bullets for smaller game, than smaller bullets for bigger game! I shoot everything with 180 grain bullets with my ought-six, because I know this load and where it goes! I shoot 300 yards or 20 and know the rifle and the load. Recoil is negligible in an Ought-six. If a 180 bothers you, get a 25'06! If you switch back and forth with bullet weight ... 150 to 180, you have to re-zero, and relearn that load. Pick one and be the master of it! The master of one load is who I count on bringing home the bacon!
In my ought-six I shoot 180, but 165 will bridge the gap between 150 and 180, and is more efficient for longer shots than both. In my .300 Weatherby I shot everything with 180 grain bullets for the same reasons, but it is faster and is efficient with the 180 at long range.
Good Luck, try other ammo, and take your time letting the barrel settle down and cool. If you are unsure of using a rest for shooting, take along someone who is to assist you. I am sure that new Model 70 will be a fine rifle. I looked them over carefully at the NRA Convention this year, and they are truly a nice rifle. I wish I were there to have a go with your rifle!
REMEMBER, a Monster Buck will only give you ONE SHOT at best! The rest of the group won't matter!
I have attached a photo of such a buck that I shot near my old house in Colorado, Divide Colorado that is. It was not in season though!
