I just assembled a 300 Blackout AR using an upper from Red X Arms. 16 inch stainless steel and fluted. 1/10 twist. Using UMC 115 grain plinker ammo I was grouping 5 shots at 1 3/8 inch at 50 yards and 2 1/8 inch at 100 on the first trip to the range. Each group had 3 shots that could be covered by a nickel. Poor shooting on my part with the flyers plus my trigger was feeling REALLY stiff and gritty. I think this upper could perform a lot better once broke in and a little more patience/practice on my part.
" The world is a very dangerous place, not because of those who do evil, but because of those who do nothing about them." - Albert Einstein, 1879-1955