If I could only have one rifle, from my current collection.....it would have to be my Remington 700 SPS Tactical in .308.
I can shoot bullets ranging from 110 grains to 180 grains and I can load the power level up or down considerably. There are also a myriad of bullets available to load in 30 cal.
The .308 is a legitimate 800 yard cartridge, but a marginal 1000 yard cartridge. Since I never shoot more than 300 yards, its all I need.
The .308 can handle any game in North America up to Elk, out to 250 yards.
My rifle weighs about 9.5 lbs with the scope and bipod....so it kicks like a 30-30, which is awesome!