The M16a2 is damn accurate out to 500 yards. I shot back when they used scoring and not just body shots. I routinely scored over 230 of a possible 250 score. Very tight groups on rapid fire. The A1 was not nearly as accurate.
I don't know the manufacturer. Will have to take a trip out and look at it again if still there.
With an AR, here's what you need to do:
Hold the rifle so that you can wiggle the upper and lower against each other. There is going to be a little bit of movement there, just because of the design, but you want as tight a joint as you can get. One that is poorly designed, or wearing out, will move very noticeably. Eventually, it may start to jam, and the only fix is a gunsmith with a manufacturer's license, because it is going to take some machining and a hefty bill to get it tight again.
Then hold the rifle and wiggle the butt joint (just wiggle the stock and see how much it moves). If it moves much at all, the threads may be wearing/stripped, or it might just be a cheaper design or a poorly matched stock. Think about it.....if the butt stocks wiggles, how accurate can it be?
That's why I like the Stag and Rock River guns. For the money, they typically give you good, steady joints at a relatively lower price. From there, ARs are pretty much all the same., You're going to trick it out how you like it, and all the parts are universal, so you fall back to relying on those two joints. Ask who made the upper. Daniel makes most of the uppers for the military now, and they are solid (there are better, but Daniel is (literally) good enough for government work).
I have a S&W M&P that I haven't touched at all. I think I paid right at $1100? It is VERY solid and well made. Right out of the box, it will be very adequate, but 300-400 or so more than the Stag and Rock River.
And know that you're used to precision, so no matter which one you get, you're going to be disappointed with the accuracy. They're just not designed for that, and in the scenario I *think* your describing for this one, speed of fire and ease/cost of ammo are going to be the bigger factors. Sounds like this is going to be an "oh shit!" gun?
Good luck, and let me know if I can help. Gunbroker.com (really any of the auction sites) is a GREAT place to look around and get an idea on prices/availability.