There are lots of AR-10s but accuracy is what I am after without having to go to some massive bull barrel set up. I’m wanting to keep to 308. I’ve been thinking about an Aero M5 build using a Rainier Arms Match barrel.  

Will the Rainier Arms barrel get under 1 MOA? Yes, I will have a good scope and Geissele trigger.

No experience with the Rainer Arms Match barrel.

I can say my Wilson Combat Super Sniper is sub-MOA on 5 shot groups, haven’t shot a 10 shot group with it, though I should.  It’s paired with an Aero receiver set.

I’d add to that, I was about .7 MOA with Norma Golden Target, which is decent ammo, but only tried one weight, I’m sure if I experimented I could find something that would shoot even better.

Not sure if that’s overly helpful, but at least shows you it’s doable with Aero receivers and a quality barrel.