Here's what got me to hop on the latest fadwagon of the 300 Blackout.
She started life from a Green Mountain minigun barrel.... Lopped off the chamber, reamed out room for the 300 Blackout case. Spent today on the lathe, cut the bbl profile, gas block deck, cut gas port, cut muzzle threads, recrowned the bbl, headspaced and fitted the bbl extension.
Now.. it's a 300 Blackout bbl that only cost $35.
Worked up a few loads, 19.0 grains of Hogdon H110 under a Barnes #30811 (110gr TAC-TX FB). Have a mag full worth ready to go, fitting the bbl to a spare upper tonight. Hopefully tomorrow I'll get time to go play with it, then teardown and paint!!
Many thanks to my buddy D.S. for the expertise, education, and my "first hit on the crackpipe" (which is playing on a metal lathe).