Okay........never mind. Using Tomme's info and case capacity for a 204 grain bullet and 2.155" OAL, 5.5 grains of Unique models about 1,025 fps from a 16" barrel. 13,000 psi max, all burnt at 4.5" and about 4,700 psi at 4.5" travel. Where's a carbine port again? 7.5" from breech face? So we have about 3,100 psi at the port, not gonna cycle.
19.0 grains of Varget models 1,072 fps at just under 11K psi peak and about 4,000 psi at the port. That's 82% of case capacity.
12 grains of Lil'Gun might do it.
But the best one I found is my old favorite Miracle Worker for ARs and weird calibers: Reloder 7. 15.0 grains gets 1,086 fos, 9,500 peak pressure....but 5,000 at a carbine port and a good long dwell to the muzzle. It will leave mummies that might cause jams if you have a suppressor, but is your best chance at subsonic loads that will cycle the action reliably. 5K at the port is pretty much minimum.
