Lloyd,
A few suggestions:
For load workup, read
Dan Newberry's whole site. He uses a round robin like Doodlebugger, but only runs 3 shot groups. More increases confidence, but he is looking for 3 such targets in a row, so really 9 shots are proving the load. As your first blush experiment showed, you will find more than one sweet spot. If a good one is close to that 23 grain load, then the lower pressure load will let your barrel's throat last longer, and the velocity is probably fine for 200 yard accuracy with light bullets.
Try the 53 grain Sierra MatchKing #1400 or the 55 grain Berger #22410. These bullets have flat bases rather than a boattails, and for technical reasons it is usually easier to get accuracy out of a flat base than a boattail when you aren't shooting at enough distance to take advantage of the boattail's higher BC for bucking wind. You'll find the flat base tends to do better to 200 yards and even to 300 if the wind isn't too high. It is easier to form jackets uniformly for match hollow point shapes than for FMJ, where high tolerance symmetry of the formed point is a challenge to achieve. Also, as Harry Pope said a century ago, "the base steers the bullet". That is, perfection of the base form is more important than perfection of the nose by a pretty big margin, and a square formed solid base with no exposed core is easiest to get that with.
My Compass Lake built NM type Bushmaster gets around 1/2 moa with either of those bullets, which is about the limit of my eyes working with iron sights these days.
Twist rate requirements depends a lot more on a bullet's length than on its weight. Bullet length is the lever arm by which air pressure on the nose in flight overturns it. Thus you'll find with your 9" barrel that you can stabilize the stubby shaped. 0.995" long 77 grain Sierra MatchKing just fine, but the 1.063" long 75 grain Berger VLD, while not outright unstable, will not make for tight groups and may need as much 500 yards to go to sleep. It really requires an 8" twist to stabilize best.
Speaking of Compass Lake,
Frank White's match trigger is in the same price range and mine works very well. More than once I've had a fellow at the trigger weigh-in at a match feel it and tell me it wasn't going to be able to pick up the weights, only to be proven wrong. It is two-stage.
A two-stage trigger has a first stage that is some slack take-up before the trigger stops against the second stage for the hard break. A single stage has no slack. I consider the two-stage inherently safer in a semi-auto simply because the reset release length is usually a bit longer than for a single-stage. Some folks can get behind a Garand or M14 and pull it into their shoulder with so little force that the gun moves out from under the trigger finger far enough to reset the trigger, then shoulder bounce pushes the gun forward far enough to re-pull it. Thus, the gun can double even with the two stage trigger. A single-stage, were it available for those guns, would have a shorter reset length and make it more likely. That doubling mechanism is far less likely with the light recoiling AR, but an ounce of prevention and all that.
