I had a fascination with the 300 AAC Blackout for quite a while. I was going to build my AR pistol in this caliber, then after looking at the bigger picture...I decided against it. Here's why: I don't like fighting the .308 guys for bullets to reload, powder is hard to come by, commercial blackout ammo is pricey, and they don't make a 110 / 125 grain FMJ plinking bullet for reloaders. Perhaps if this all changes, I'll revisit the idea of getting a blackout upper, but until then, I'll stick with 5.56. Don't misunderstand me, I do like the cartridge, they just need to start making the ammo & components more available.