So first, the good news:
My 300BLK upper will feed flat nose bullets.
The bad news:
I can't seem to get them to shoot worth a darn.
Here's the story. I recently bought a Lee C309-170FN mold. It is made a lot better than the older ones and has nice vent lines. It seems to really like being run hot, as I couldn't get good mold fillout until It was hot enough that I had to wait a good 7-8 seconds for the sprue to harden.
Alloy: Indoor range scrap consisting of a lot of 22, jacketed pistol bullets, and commercial cast lead. Unknown composition but it weighs very similar to 50:50 WW/Pb and other bullets cast with it perform well.
Mold: As stated LeeC309-150FN. Dropping at .311-.312 and 178gr.
Copper gator check and Lee Alox tumble lube. Push thru sized at .310
Loaded in converted, mixed headstamp 223 and 5.56 brass over IMR 4227 at 14.1 and 15.3gr test charges.
CCI #41 primer. OAL 2.040"
Platform: Frankenstein AR15 pistol. 12.5" CMMG 1:7 pistol gas barrel. Vortex Strikefire red dot with 2x magnifier. Liberty Mystic suppressor.
Position: Butt on ground, gun on lawn chair.
At about 60 yards I am getting 3" wide by <1" tall groups.
this is the 14.1gr load
the 15.3gr load. I dont know about the flyer. I may have pulled it.
I'm going to try it without the suppressor, although it never has affected group size before, just POI.
I'm going to try it with a better rest. I will have to set up a table, and get my sandbags out.
Started raining, so I wasnt able to complete my testing, but I wanted to get some feedback.
This gun will group 1" @50 yards with weight sorted C312-155s. About 1.5" with unsorted boolits. Dunno why the horizontal stringing with this new load.