I never tried to make mine a precision rifle, but I did feed it some handloads with Nosler 168gr BTHP over RL15. It was around 1.5" at 100 yards.
The thing about the M1A is that it really is not the best choice if you are wanting to mount optics. The rail system has too many places to to go sloppy, and the stock geometry is way too low at the comb. You will need a cheek riser of some sort or an aftermarket stock. The AR-10 is so optic-friendly I wouldn't even consider an M1A if optics are on the menu.
