I have 5 barrels I shoot with a suppressor; I have 2 Gemtech 30 cal suppressors, you can shoot smaller calibers through them very effectively. I have 22LR, 5mm Rem mag, 22 hornet, 25-20 and 300 BLK. The 22LR sounds like an air rifle even through the 30 cal suppressor. The number one thing the suppressor does with subsonic loads is get read of the supersonic crack of the bullet and the blast of the fired round. With supersonic rounds you will still get the supersonic crack of the bullet as it breaks the sound barrier but elimates the crack of the fired round. If you choose the 300 BLK all powder manufactures have subsonic load data for it, if you want to hunt with it, I recommend 220 round nose either Sierras or Hornady's, from shooting the 300 Whisper and then the 300 BLK since the late 80's it performs much better than the pointed bullets, the round nose bullets will tumble and cause massive internal damage whereas the pointed bullets just drill a hole with much damage. On broad side shoulder hits the deer mostly just drops right there or maybe take a couple steps then piles up using those round nose bullets.

You just can't keep reducing minimum loads to get subsonic speeds, some powders you can't reduce the minimum loads more than around 10%, check your reloading manuels to make sure of the powders you can use in subsonic loads. Some powders have subsonic loads listed in their manuals.