I agree with Graybeard, a long shot takes everything he mentioned and a little more. Wind of any strength, animal movement, mirage, can negate any shot made by an experienced long range shooter, let alone someone that doesnt have a clue of want 400 yards really is. I practice on a silhouette range regularly. I know what 200, 300, 385 (421 yards), and 500 meters (547 yards) looks like. Taking a shot at a steel target with the objective of just hitting it and pushing off a rail is totally different from placing a shot in the vitals of a big game animal.
Although 7mm BR, 308 Win, 260, 270, and 280 have all been used with various success as a silhouette target caliber, IMO they fall short of being a long range big game rifle caliber. IMO a caliber that shoots a bullet with enough weight to still have the energy needed by the time it gets to 400 yards with the shortest amount of flight time is called for, unfortunately all that come to mind have Magnum at the end of their name.