I'd be building it for more of a short range/home defense gun. Probably 8.5" barrel. Eventually get a suppressor.No worries... just trying to provide a bit of insight from my experience.
I would recommend finding one specific and popular subsonic and one specific and popular supersonic that work well and stick with them. That will greatly reduce the chance of unreliable performance.
For me, I went with Remington for both. Since the AAC engineer went over to Remington, I figured I would give them a try. Their 120's and 220's are very consistent I can can find them everywhere, including Wal-Mart. Of course... those are just examples.
Good luck and looking forward to hearing the range report!
If I am buying a new complete rifle or pistol in 300 Blackout over the counter and AAC can't be found, "today" I wouldn't buy anything but a Daniel Defense.
Building with what we have available today? ...
AAC barrels and gas blocks are still floating around. I would start there. If you don't find a length you like (supply is getting thin) I would get a Noveske.
Alexander Arms has nice uppers. They are machined very well.
I like BMC uppers and lowers also. They are very good quality. I have a Bravo Company lower that I put heavy use on, with frequent trigger changes, and I am not seeing any since of elongated pin holes.
Most rail systems don't matter much... but stick with free-float. I'm partial to KAC.
I also like Bravo Company BCG's.
As far as I am concerned... no other triggers exists for AR's except the Geissele Super Semi-Automatic Enhanced (SSA-E) trigger for precision (2-stage) and the Geissele Super Dynamic 3 Gun (SD3G) trigger for extreme speed (single stage). Screw all the others.
Also, if you want reliable minute of man out to 350-400 yards, get the low-profile Bravo Company fixed A2 front sight and low-profile carry handle rear sights.
Troy or Bravo Company ambi charging handle.
Stocks, grips, tubes, etc... shooter choice.
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