Unique will work in subsonic
 

I decided to try it since I couldn't find any information. M1Sales upper on a RRA lower, will cycle my regular load of 4227 w/ a 220gr SMK. I don't have a crony so take the info for what your paying for it.

LC 223 brass resized, CCI small rifle primers, 220 SMK.
First I tried 4.0 grains of unique, no pressure signs on the case, bullet was slow but cleared the barrel. Then I tried one at 5.0 grains of unique, much faster, a little more noise and some recoil, the primer started to flatten out. At no time did the action move. For a bolt gun this round could be a lot of fun, I'm louder in the wood shop than when I was experimenting.

Just putting it out there Unique will work, just not for what I want.

I have been using Unique for quite some time with cast bullets and light bullets in the 30-06.
When I got a bolt in 300 whatever I started with Unique with both cast and jacketed, stuck a few but have had great fun with Unique. Shoot all day on 5 to 6 grains per round.

Unique
 

Unique is my hunting load for my 458 Socom, 13.2gr Unique and 405gr Rem FP. They don't cost much for targets and you can shoot a 200lb. hog length ways and most of the time it comes out the other end. It is a little louder than Trail boss out of the suppressor, but more consistent.