In .308 or 30-06 you can use pretty much anything to shoot paper. I would first find out the rate of twist in the barrel. 1:9 can generally handle heavier than say 1:11. For hitting paper, the lighter 140 grain will recoil less than the 180 grain. In the same thought, the .308 uses less pouder so it is usually cheaper and less recoil also. I have both, but the 30-06 has not been to the field in 8 or more years for the recoil reason. I can shoot the same bullet for less from my .308 and kill paper and animals both very quick.
For lighter ammo look for the Varmint loads, could be as low as 120 grain in 30-06, 80 grain in .308. (just what I have seen more common for factory loads)
Nikon, Bushnell, and a few others. Tasco and BSA have both lasted on 30-06 and shoot well at 100-200 yards for hunting and light target. This is a BSA on one of my 30-06 bolts and shot well out to 400. Never tried that rifle past that.
Your budget and pourpose would dictate more of what is a good optic. If I were to go Long Range, I would consider completely different optics.
