well i am just about done with my 300 blackout upper and i am gonna start loading up some test rounds. i have h110 and i have 1680, mostly for now i am gonna be loading supersonics until next tax season when i can order my first suppressor. i have formed 50 pieces of 223 and 50 5.56 for the blackout and i just ordered some 125gr nosler ballistic tips. i am thinking of making some up with 17.5gr of h110, the nosler 125's and an overall length of 2.12 00 i am also gonna order a box of umc factory ammo to do the initial testing but i want to get started on loading too. any info would be great. as for the 300 blackout i am building here is a parts list of what i have together so far.. daniel defense stripped upper w/ dpms parts vltor gunfighter charging handle medium midwest industries SS series customizable tube ext carbine length stoner 16" ultra-lite barrel w/dsa trident flashhider yhm lo-pro clamp on gas block dpms gas tube all i need to finish is the bcg, most likely gonna be daniel defense. as for now it is wearing a leupold prismatic until i can figure out what optic i want to use.