I'll have to concur with flinch that the triple shock is not the bullet for the .308 at extended range. The triple shock is a great bullet if you are going to be launching it out the muzzle at 3000 fps or more, and you keep the impact velocity at 2000 fps. In a .308, a 165 or 168 gr pill is doing at best 2800 fps from the muzzle, and I don't have any balistic charts with me, but believe out around 300 yds you'll be dropping below 2000 fps. If you go with a softer bullet such as a balistic tip, you'll still have a strong enough bullet for 2800 fps at th muzzle, and get reliable expansion down to about 1700 fps.
I think this is a backwards approach to a long range hunting rifle. First pick the bullet you want to use, then figure out what velocity you need at the longest range you expect to use that bullet, then look for a parent case to launch that bullet fast enough to get the desired terminal velocity at your max desired range.
I don't see the .308 being a 500 yd big game round. While there may be minimum power requirements for ideal shots in an ideal world, the real world presents situations in a slightly different manner. Better to have a bit more gun just in case.
I'd also say generally those with the skills for taking game at 500 yds don't need to ask questions about suitable equipment. They also would not choose a .308. If one can afford all the proposed hunts, then one could certainly afford a 300 magnum, and be much better served for the task at hand.
