300blk is hit or miss on the accuracy. The chrono numbers are also all over the place. However it seems that even though the loads are not consistent, some times they are the most accurate loads guys show, while loads that are pretty consistent across the chrono are not at all the best accuracy loads out of the gun.
It takes work to get decent accuracy loads.
My 208 AMAX subs shoot MOA fairly easily. They are more accurate than the 220g SMK subs, but not by much. A buddy that loads and shoots 300blk also shoots 208 AMAX sub MOA(I think he had 5 rounds at 100 into a hole the size of a soda can tab if I remember what was sitting next to the holes in the picture). I have put 2 into one hole on many occasions. My buddy called a miss on Monday when we went, but when we got the target it was 2 into one hole.
I have seen the new 125g SMK supers showing good promise as well as the 110g Barnes(although they are pricey). I think the 125 noslers are doing pretty well too. I dont load supers to much though.
A lot of it is in the brass prep IMO(although I dont do much except full length re-size and trim). Some guys say they have better luck when annealing the brass after forming. Some guys are neck turning. I personally havent done any of that. I just run my cases into my forming/cutting setup(from Brads Warehouse) and then run em through a Forster full length sizer. I also use a Lee FCD for crimping and put a decent crimp on my rounds, some guys dont crimp at all.