I built mine in late January. Like MWP said, the parts are out there and, imo, worth the trouble of putting together. I chose a 22" SPR contour barrel-rifle gas, Vltor upper and Geissele 15" handguard. I chose that length as a compromise of trying to maintain as much length as possible for velocity, but not have it ridiculously long with a suppressor on.
The combination of the ARP bolt and barrel extension, the small primer pocket, and the overall excellence of Lapua brass allow you to run pressures/velocities that are beyond most other small frame AR combos. Yes. Losing brass is painful: use a brass catcher!
I first tried 55gr Hornady SPSX's with Varget since I had a lot of both around. While they worked(not a real surprise, but they were pretty rough on reds) and I was able to get decent velocities, my initial goal was to have as flat of a trajectory as possible for night hunting so I ended up settling on 39.1grains of ARComp behind a 40gr NBT. This produced 4320fps out of my 22" barrel. A bit below Bruce's max, but the next node was too high in pressure. Do the math on that BC/velocity: it's FLAT... For an AR especially.
So far, it has dropped 2 yotes, a handful of reds and various coons, opossums, and skunks. Young coons, possums, skunks are pretty messed up. Fat winter coons, coyotes, large fox are all minimal or no exit. Shoot them around the edges though and all bets are off!
It's not a difficult round to load for. Just necking down and some initial trimming. No neck turning was required. The only 'special' requirements were some deburring of the extractor and the preemptive use of an adjustable gas block since its run suppressed.
I anticipate many loadings per case. I'm over 10x fired on my 6x47L Tikka/Bartlein/Manners cases. I used one lot of this brass and it's now 3x fired Hellcat brass. Primer pockets are still tight. Several annealings at this point though.