You are focused on energy. Yes, 270 ft-lbs is about double the muzzle energy of a .22LR, but you neglect to take into account that low terminal energy is due to low terminal velocity, and low terminal velocity equals longer flight time, which means more wind drift. Not to mention the 166 FEET of holdover.
The .308 is not a 1700 yard cartridge, no matter how you slice it. It loses too much velocity.
"Yes, 270 ft-lbs is about double the muzzle energy of a .22LR, but you neglect to take into account that low terminal energy is due to low terminal velocity, and low terminal velocity equals longer flight time, which means more wind drift. Not to mention the 166 FEET of holdover. I focus on energy. because energy is what causes damage, "low terminal velocity" or not. Read up a bit on Civil War snipers and see what kinds of holdovers and windages they had to contend with. The target is both big and fragile. A hit almost anywhere with 270 ft-pounds concentrated in that small area is very likely to cause non-survivable damage.