I have a regular Ruger American .308 that's right at 1 MOA with basic handloads (nothing fancy like neck turned cases, match bullets, or competition dies). The only modification I made to it was sanding the barrel channel in the stock to prevent contact with the barrel. The major downside of the normal American is the super thin barrel that heats up quickly so it doesn't stay 1 MOA for long.
I bet you could get less than 1 MOA with the heavy barrel American in .223. Just be aware that the American is a budget rifle, the plastic stock is flimsy, and the mags are way overpriced for what they are. I guess what I'm saying is while the Americans are accurate enough and I'm happy with mine, don't expect the American to have the solid feel and overall quality as a higher priced gun.