Mike. Look on Midway and put yourself on the wait list, I have gotten several boxes of ammo in 300 from them since the ammo shortage. Put yourself down for an email and text. When you get the text, order immediately cause it goes quick. But you can start stocking up that way.
I won 200 rounds of the 220gr ammo from these guys on 300BLK forums. It ran exceptionally with Lancer Mags, Magpul didn't lock back a few mags, but else flawless. Chrono thru 8" CMMG w/ Octane 9 HD suppressor @ 1025ish, max was 1050.