300 blackout is a silly round, without either the ballistics of the .223 or the 7.62x39 but with the price tag of both combined! Feeding issues, stabilization problems, limited range...just another fancy wallet lightening device
stick with the prescribed remedy AR-10=.308 AR-15=5.56/.223 AK-47=7.62x39 never 12g
when we start fiddling with platforms expecting them to be something they are not we end up drastically limiting the effectiveness of the system for example Defender size 1911s (cycling issues) or PUV's (haha)
Long story short there is no "do-it-all" rifle, it's like playing a whole game of golf with a putter.
I may ruffle feathers but this is what I do for a living and I'd hate to see any of my VX buddies wasting money/being under gunned/acting like CoD crazed mall ninjas
For the record, 300 Blackout is fun especially suppressed, but so is 5.7, .243 Shehane, 500 NE, .223 ssm, .457 WW you get what I mean, fun is fun, practical is what you lean on when it's really needed
Have fun, spend your money the way you like, enjoy life