Hi Tuckerjoy.
You're taking on a graduate-level project with jr. High information. I'm gonna throw some things out there and you tell us if and where you get lost.
First, you need to fit the bullet to the rifle. Not the bore/groove, that means nothing. The meaningful fitment happens in the throat of the barrel. That means you need to know the chamber neck and throat dimensions of the rifle, which means make a cast of it somehow and get those measurements. Forget bore and groove fitment, if you want any kind of accuracy at the higher velocities necessary for reliable function, you have to think in tjree dimensions and not just two...and fit the throat. Also, forget jamming the bullet in the lands or trying to make a bore-rider fit, it just won't wirk fhat way with an AR and the weak camming action. The bullet needs to be free from contact when chambered, but still be "right there" to touch something the instant it moves out of the case neck.
Next you need to prepare your brass to hold the bullet correctly for the size it needs to be. Bushing neck sizing dies excel at this, standard dies do not because they overwork the necks off center. You will need an expanding/bellmouthing die of exactly the correct diameter also.
You will also need a good, straight-line seating die. If you cannot make concentric ammunition that fits your rifle the way it needs to with cast bullets, your results will not be good.
Forget the "reduced rifle" type powders. Use real rifle powders like you would with jacketed bullets. 3031 and 4895 are good, so is 4064 and Varget or even H414 and 4350. Try for at least 2000 fps with 3031 and it should cycle just fine and still be in the "easy" zone for accuracy.
Alloy.....19 bhn is plenty and then some, but how it gets 19 bhn is more important than just the size of the dimple the tester makes. Couple ways to go here, I like a low-antimony, lower tin alloy bumped with heat treatment, but something like Lyman #2 or Taracorp Magnum, water-quenched, is also good. Main thing is you don't want the bullets to be too brittle. Tough is good, brittle is not.
If you really want to cheat and skip to the end with 1.5 MOA groups out to 300 yards at jacketed velocity and no fuss, I can give you the exact recipe. It involves about $500 in new tools plus a custom nose bump die you'll have to make, plus learning a new process, but it works really well.