Since this in the "Other Rimfire" section, I'll stick to rimfires. It would have to be my dad's Remington 550I. Remington made very accurate rimfires in their heyday, a time long since passed.
I understand. I had a Marlin XLR in .30-30, which are notoriously droopy. Three shots all touching inside a quarter at 100 yds. on more than one occasion. No one would believe that except the guy who witnessed it.You all can call me crazy. I shoot 3 shot groups and if I do my part with the right ammo I can hit 1/4 moa at 100 yards (not every time). I mostly average around 1/2 or so moa at 100 yards with it. Naysayers will say it's not possible all day, and honestly I'm still amazed every time. Argue it all you want, doesn't change the fact! There are so many factors that go into it. This is also at an indoor 100 yard range with zero wind factors. At my outdoor range, I tend to get closer to 3/4 to 1 moa at 100 yards.