Those 69gr SMK bullets are a great choice, and should be a good match for that 1/9 barrel.
When I first got into building accurate rifles, an old gunsmith taught me the "3 B's" of accuracy - Barrel, Bedding, and Bullets, and that everything else is secondary. In my experience that applies to an AR as well, assuming we're starting with a free-float barrel system anyway.
- A good accurate barrel is the heart of an accurate AR. For accuracy, a free float handguard system goes hand in hand with that.
- The "bedding" part is the fit of the barrel in the upper receiver, and in my experience there is definitely a difference between a loose fit and a very tight fit. I like the BCM interference fit uppers best for this (you heat up the upper to fit the barrel extension into it; it's basically a press fit). Loctite or epoxy to bed the extension in a looser upper is next best, and a drop in fit assembled dry is at the bottom. Strictly speaking to accuracy here, not reliability or function.
- The importance of bullets is obvious to anyone who loads their own and has worked up an accurate handload. If you don't load your own, experiment with as many different types of quality ammo as you can get, and buy a bunch of the most accurate load. You may want to write down the lot number of that ammo if you're real picky.
A good trigger, gas system tuning, stock and optic choices, etc all matter too, but IMO the three things above are the platform to build an accurate rifle on.
