So I've been playing with some 300blackout loads recently. I had multiple goals when I started this build... -find out if it can be used as a hunting round -build a sub-sonic round with some punch -create some plinking rounds *these rounds are being fired out of an AR platform rifle, 16" barrel with 1:7 twist, carbine length gas system and auto BCG. #1 - GOAL: this was intended to be a subsonic round (the plan is to obtain a suppressor down the line) *i realize the suppressor will give me different data, but i wanted to start out with a base subsonic load and then build from there. BUILD DATA: Nosler 200gr Accubond 10.5 grains of IMR 4227 CCI SRP #400 2.250 overall length PROJECTION: 1100 fps, 537 ft/lb ACTUAL DATA: -average velocity was 1194 fps -based on the ballistic calc this round produces 633 ft/lb of energy NOTES: -Failure...runs too fast to be subsonic -Failure...this did not cycle the bolt enough to chamber a new round but it did push the bolt back far enough to eject the spent case. -recoil was very light The plan is to lower the powder charge and try seating the bullet further into the case...will be going after a 2.220 length in hopes of increasing the pressure a bit so it cycles reliably. #2 - GOAL: this was intended to be a hunting round/plinking round BUILD DATA: Hornady 165gr SST 13.5 grains of IMR 4227 CCI SRP #400 2.216 overall length PROJECTION: 1550 fps, 880 ft/lb ACTUAL DATA: -average velocity was 1548 fps -based on the ballistic calc this round produces 878 ft/lb of energy NOTES: -rounds cycled flawlessly -projected data matches the actual data almost identically (very happy about this) -good for plinking Planning on increasing the powder to get more FPS as this doesn't have enough velocity to give good expansion of the projectile. Next round...16 grains of powder. FINAL THOUGHTS: I'll be tweaking the formula a bit for the subsonic round and if I can't get enough FPS out of the hunting round I'll be replacing the 165 grain projectile with a new lighter projectile. The new projectile that will be added to the mix will be in the 147-150 grain variety. I like the Hornady SST bullet so I may stick with that or find a good soft point. I'll update this thread as time goes.