It's SUPER easy to make your own brass, if anyone wants to. 223 brass can be had on the cheap (or picked up at your range) and with a small saw and jig, it's fast. I followed a thread on 300blktalk and go the Harbor Freight saw, one of the jigs a guy was selling, and I've never bought a 300blk case yet. All it takes is your time.
And seriously, if anyone wants to try the 203g projectiles, I have just short of 1500 of them (buddy talked me into a big batch, then when I started having issues he bailed!). If you pay the shipping, I'll send you 25 or so to test. If they work for you, then I'll make a deal on the rest.
I use H110 for my supers, and A1680 for my subs. I know guys are using H110 for both, but there are warnings about loading H110 that low or so they say. I also found A5744 to be good for subs, and LilGun good for supers.