I have 2 308 pistols w/12.5" barrels I will post a pic or two when I get home I think the rails are 10". 308s do not have an inside voice. Torch that off indoors w/o ear pro and you won't be hearing anything for a long while.
This will work. If you don't like this stock you can order just the buffer tube, buffer and spring and install a fixed stock from somewhere else.
https://www.armalite.com/SACItem.aspx?Item=EA6050