I think one thing is that all ammo has gotten ridiculous.
My point is maybe in line with yours: 300 BO may never become “the 7.62 x39 replacement”.
Yes, the 5.56 may be the better long term solution for the average person wanting a battle carbine.
And yes, a 9mm carbine is much better in most home defense scenarios today.
Ammo pricing's starting to come back down to normal levels n most domestically produced calibers, but 7.62x39 really isn't due primarily to the Russian import ban -- that was my point.
My point about 9mm was just training -- you need lots of rounds to reach confidence/proficiency w/ any weapon system and why for instance, I'm so confident in using a 10/22...
For many folks, especially those new to firearms and on a budget, the cost of gaining proficiency is a huge deterrent.
Vs. 5.56 or 7.62x39, 9mm is significantly more affordable (and 7.62x39 used to be similarly affordable as 9mm, allowing for lots of rounds down range and 7.62x39 platform proficiency development for many, myself included).
I think .300 BLK is already the 7.62x39 replacement for ARs, especially compact/subcompact ARs. But because of kaboom risk, I personally prefer 7.62x39 which necessarily leads to something more along the line of a CMMG Mk47 if wanting a more modern platform w/ AR levels of configurability -- but because I like historic design, engineering, and history, I find the Vz58 much more satisfying, but with inherent limitations, while still allowing chambering 7.62x39, but I acknowledge that others may have different requirements and expectations...
I truly don't know what will happen insofar as 7.62x39 versus .300 blk ammo availability and pricing, but 7.62x39 should have more staying power, if only due to the relative ease with which .300 blk ARs can swap barrels (and most combloc rifles are a much more involved exercise) and the steady and pretty much constant introduction of supposedly new and better calibers in the AR world... Me personally and not to beat a dead horse, but the kaboom risk of 5.56 and .300 blk just makes .300 blk a nonstarter for me. If I want something suppressed and subsonic, .45 ACP has nearly identical ballistic performance in every way except penetration vs .300 blk, and if I want something supersonic 7.62x39 can do everything .300 blk can do (and historically has done so for half the cost of .300 blk)...
YMMV.
