This custom built .243 win on a Remington model 700 action would be my choice. Using 105 gr Hornady A-Max or 115 gr DTACs, this .243 win will shoot inside many larger magnums from 0 - 1200 yds. Load up some Barnes TTSX bullets, and you'll be good for just about anything in the lower 48.
Remington model 700 action
Holland lug
Krieger #5.5 contour barrel
McMillan HTG stock (pillar & glass bedded)
Shilen trigger
R&D Precision DBM trigger-guard (accepts 5 & 10 round AICS magazines)
Badger 20 moa rail
Seekins Precision rings
Leupold MKIV 4.5-14x40mm