I normally only shoot 3 shot groups with sporter weight barrels. I did shoot 5 shot groups with heavy barrel rifles and varmint cartridges. As for 1 inch groups, my Model 70 Super Shadow has managed to shoot a lot of groups under an inch, some of them way under. But any single group is pretty meaningless. I try to shoot at least 3 3 shot groups with the given load, obviously the more groups that are recorded, the better. And I believe I could go out to the range tomorrow under reasonable conditions (semi calm wind, not too hot) and shoot 3 or 4 groups with it and its' preferred load and average under an inch for those groups. Now I have a 6.5x55 Howa that has shot groups as small as .225 for 3 shots at 100 yards, but has a tough time averaging 1.5 inches for multiple groups. I swore that I would get a load for it that could make the 1.5 inch average or I would sell it. I think I am there. Guess I need to go to the range tomorrow and make sure that I am still there.
I guess my point is that any rifle can shoot a one inch 3 shot group at 100 yards. If you shoot enough groups, you may even get one group that is only a half inch or a quarter inch. One group means absolutely nothing. Conssistency is what we really are looking for and a rifle that can shoot 3 three shot groups that measure less than 1.5 inches is better than a rifle that shoots one half inch group and two 2+ inch groups, even though they "average" the same.