Looking at buying my first 308 this winter and started looking at reloading tables for the lighter bullets. My question is: When using the lighter bullets, do you lose accuracy to get higher FPS? More specifically, if I use 130gr bullets will my 4 shot groups at 100 yds be larger than 180gr bullets? I want this to be my primary deer rifle and match my 270 win in performance if possible...
Only your rifle can tell you that. I have a .308 with a Pac-Nor barrel put together by Mickey Coleman and the bullets it loves the most are the Nosler 125 BT and the Sierra 125 Spitzer. It shoots 150, 165 and 168 grain bullets pretty good but is a bit finicky on the load and bullet style, but it shoots those 125 grainers into little groups with a variety of different powders and charge weights.
FWIW, I've found the Sierra 125 grainers to be accurate in just about every .308 and .30-06 I've tried them in, this is going back 35 years. Possibly a bit too lightly constructed for what you want but I wouldn't be afraid of ligher .30 caliber bullets at all.