The terminal ballistics of 55gr .223 in FMJ are well documented. I think the case could be made that if you're going to hunt deer with a .223, then FMJ is at least as good as the alternative bullet types, in spite of the fact that it goes against conventional wisdom and hunting regs in some places.
In .308 there are an assortment of better alternatives to FMJ, and no-one would recommend FMJ for hunting.
All that said, no one would dispute that .308 FMJ is better suited for deer hunting than .223 of any variety.
(Anecdotal data point: FWIW, I took one small whitetail with Remington "powerpoint" pointed softpoint 55gr .223 at about 90 yards. It hit the lungs, and the deer moved about 15 yards and collapsed. )
In .308 there are an assortment of better alternatives to FMJ, and no-one would recommend FMJ for hunting.
All that said, no one would dispute that .308 FMJ is better suited for deer hunting than .223 of any variety.
(Anecdotal data point: FWIW, I took one small whitetail with Remington "powerpoint" pointed softpoint 55gr .223 at about 90 yards. It hit the lungs, and the deer moved about 15 yards and collapsed. )