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Yeah 300 Blackout is mostly about why you would want or need it (unless of course one just has money to burn).
For me, I wanted to add 30 cal to my AR Platform and everything but the barrel is the same, so no new mags, no new BCG, no new Lower, etc. I would rather hunt Boar or Deer if using an AR Platform with a 110 grain TTSX (or larger) then with a 62 grain HP. Also I feel better about Home Defense with a 30 round magazine of 220 grain 300BLK then 62 grains HPs (not that 30 .223s wouldn't get the job done for I usually hit what I aim at).
I also reload so practicing is not as expensive as buying cartridges off the shelf. And of course I don't shoot 300BLK as much as .223 but again the motions are all the same since its the exact same mag and lower so it is sort of like changing out a 223 Upper for a 22LR Upper to shoot cheaper. I bought all my home defense and hunting rounds at gun shows or online mostly. I was not in a hurry so I could wait until it was a good buy or there were sales or over-stocks because I have my reloads for plinking and practice. The added bonus for those that reload is if you shoot a bunch of 223, one can reload in 223 or cut the case down and reload in 300BLK.