Re: 12" POF
It is possible to get outstanding accuracy from short-barreled rifles, but because of the enormous sacrifice in MV, you lose maximum effective range quicker.
Here are some numbers for thought:
FGMM 168gr SMK out of the 12" P-308 average 2313fps according to POF
178gr A-Max out of the 12" P-308 average 2311fps according to POF
I would estimate (I haven't done this with a 12" barrel so don't quote me on this) that you could get a round like the 155gr Scenars or 155gr Palma SMK bullets to around 2400fps or perhaps even a little more.
Using that data provided by POF (and my 2400fps guesstimate), you get the following figures (MOA adjustment based from a 100yd zero):
168gr FGMM - subsonic at 796yds and 38MOA got get to that range
178gr A-Max - subsonic at 942yds and almost 47MOA to get to that range
155gr Palma SMK - subsonic at 850yds and 39MOA to get to that range
155gr Scenar - subsonic at (an amazing) 1020yds and roughly 49MOA to get to that range (this is one of MANY reasons I am really starting to run the Scenars more and more)!
Based on those numbers, getting to 700yds is more than possible, but with everything involved with long-range shooting, your mileage may vary.
I'm not going to make any guesses about accuracy at that range, but I will say that my 20" P-308 is sub-MOA accurate including out to extended ranges. The 16" I have fired was MOA out to 600yds. The POTENTIAL for accuracy with the 12" P-308 is there, but I'll defer to anyone who has actually stretched one out that far and their actual experiences in terms of accuracy.