The .300BO is such a versatile round, but so much depends on the thousands of variations possible from projectiles, to barrel length, to suppressed or no, and so on. Assuming that you are talking AR only, I've discovered that nearly every projectile can be loaded sub-sonic. The real question has to do with "do you want the AR to cycle?" I've loaded 120gr TJ Conevera Powerbond RN projectiles with 11.4gr IMR4198, they fired...didn't cycle. Fired fine and were accurate to the 23 yards I'm limited to indoors. No chrono, but Sierra lists that load to be around 1020 fps from a 16" barrel. I got it to cycle with about 11.8gr, but not reliably...and that should have been about 1070 from a 16" barrel. Since I'm shooting 8.5" and 10.5" I'm pretty confident they didn't break 1000 fps. I've tried all of the powders I listed. If you have an iPad I’d suggest the Sierra reloading app. It is superb...it list about every powder usable with 300BO, and a large assortment of Sierra projectiles. I try to match profiles for other projectiles and try out the various loads they list, supplementing that with data from the Hornady iPad app. Makes for some fun load work ups.