If a rifle won't shoot a flat based Sierra, the chances of it shooting much of anything else plummet. The flat bases tend to be very tolerant of distance to lands, making them ideal candidates for factory ammo that attempts to shoot acceptably in as many different rifles as possible. Heck; its the easiest way to make an accurate combination for ranges where accuracy isn't very important at all.
By the time accuracy matters a little trajectory and wind matter a lot.
