11 test rounds were fired at a local range using a friendly neighborhood SDN-6 suppressor. No signs of excess pressure on any cases. The cartridges fed out of a Gen3 PMAG30 with no problems.
The bolt cycles but does not lock open (no BHO) after the last round clears in a 16″ Model 1 upper with a 1:8 barrel twist (if you somehow ended up with a twist slower than 1:8 or 1:10 it will be frustrating if not impossible to stabilize a subsonic projectile).
There was one potential keyhole but I cant tell for sure. This range is really splashy and I regularly get splash rips in targets– UPDATE: I tried another 15 rounds today – heavier crimp this time but no keyholes and decent accuracy (T1 turned out to be pointed a few clicks left – I figured that out after this group and the can shifts impact about 1″ downward).
As always with load recipes YMMV so consider this a starting point, be cautious and be safe. Chrony results can be found here.
A word on powder: Accurate 1680 is tough to find sometimes but the powder density matches the case capacity very nicely in the BLK. More on alternative powder options here. I use CCI primers because they are a bit faster burning than Winchester and that’s handy for subsonic loads to help ensure you maximize ignition to help cycle the action.
These projectiles came from Hunters Supply and as mentioned below are 235 gr soft point cast boolits. No gas check on these. They cost about the same as 220 gr SMKs but expand much more nicely:
KB ALERT: Winchester or a similar, harder primer (iow avoid Federal primers for more reasons than the name) are the only safe ones to use in a Lee Progressive loader-be sure you use the correct type of primers with a Lee Progressive system. Make sure you read up on what sort of primers are safe for your loader.
I run this load recipe on my Lee Precision 4-hole Turret Press and am using a mixture of RP factory BLK brass and Reformed 5.56 brass (LC and PMC- note that not all PMC brass has the proper casewall thickness to work for BLK) trimmed to 300BLK specs.
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Caliber: 300 AAC Blackout (300 BLK)
Projectile: 235gr cast soft point, no gas check
Primer: CCI Small Rifle Primers (no. 400)
Measure: 10.8 gr
Lee Auto-Disc setting: .71
Min OAL: 2.220 in.
Max OAL: see discussion below
my optimal OAL: 2.223-2.227in.
Crimp: I am experimenting with crimp to help secure the projectiles so they chamber as expected. I will update this when I have results
Here is my thought process to arrive at the OAL settings I use: