So what I found out was this upper was available separately or on AAC's MPW rifle that they made years ago when they were making rifles. Found some links to articles on that rifle:
https://www.personaldefenseworld.com...ockdown-power/
https://www.gunsamerica.com/digest/s...k-full-review/
The MPW was made in 9, 12.5, and 16" barrel lengths.
Here's an old ad for the upper by itself with a picture (obviously out of stock at this point):
https://www.cheaperthandirt.com/adva...128006848.html
The specifics I can find are the following:
-KAC URX III 8.0 forend, P/N 30210
-9" 1-7 twist nitrided 4150 barrel
-5/8"-24 muzzle with 51-tooth 3-prong flash suppressor
-Nickel-Boron UCT EXO BCG
-Bolt is Carpenter 158 phosphated / shot-peened w/ green o-ring
-Standard charging handle, forward assist, upper has T-marks and is lettered "300 AAC BLACKOUT (7.62x35mm) ADVANCED ARMAMENT CORP."
-The rail has the standard KAC markings and name, and is also marked AAC with the AAC logo on the forward right side of the upper quad section
Your opinions welcome. I'm ambivalent about the .300....might be fun, and here's a way to shoot it...but is it worth more selling? There aren't any current or completed listings for AAC MPW's with the 9" barrel; there are some for the 12.5 and 16's but unsure what the value on those is relative to the 9.