I looked at Rock River Arms as a starting point for what I wanted to build as I had determined that I wanted the Rock River Arms two stage trigger group.
No knowing how the 24” bull barrel would compare to the 20” bull barrel, I got both. I wanted the .223 Wilde chambering because it removes a lot of confusion about “can I shoot this mill surplus stuff?” Even though I hand load for accuracy. The 24” barrel is like lugging a railroad rail around, but is rock steady. 20” is still hefty. 18 would be fine too, I am sure.
I found both to be equally great accuracy for factory barrels, each shooting 10 rounds consistently under a US quarter at 100 rounds from a simple sandbag rest on the bench, with hand loads. It was super easy to simply bolt together a sub-moa at-15 although it did take two trips to the range to pick an optimal load. (Simple. Crazy simple)
I had never “built” a firearm before I built those two ARs. Now I would say I “assembled” them as it was more bolting together LEGO blocks than any sort of skilled artistry. I got the how-tos from a website that’s basically “ar15” and you guys know which one.
I think the essential parts for a very accurate varmint style rifle are the barrel and the trigger assembly. I got RRA bolt groups, uppers, gas blocks and all that stuff and lowers. Grips, stocks, buffer springs, fore ends... I got all over the place and lots of them second hand.
Anyways, RRA isn’t cheap but both rifles bolted together without a hint of fussing and passed their go, no-go tests immediately and within 3 weeks of lazy assembly and reloading I had two sub moa varmint rifles.
Oh, I was using Swift 8-18 40mm scope. Cheap but good.
Now, if not looking to build at all I’d get a Ruger because if you can’t wrench it yourself I know their customer service will take care of you.
That said, you pay for that service and instead I got a barrel wrench, some punches and go no go gauges instead.
Things that matter: barrel, trigger group, bolt and bolt assembly
The rest is just cosmetics holding them together, pretty much.
In the end, when you say you want an accurate AR, the question is “what is it for” or “how heavy” and “how accurate” and “what kind of sighting do you want?”