Haha! We did test fire a .223 in a steel building once just to see what the suppressor did for noise reduction. That was hilarious. The echo and shock wave from the supersonic round over 300 feet to the backstop was excruciating. I had my ear phones on but the guys I was with thought the suppressor would do something. It didn’t.
Yeah, using sub-sonic .223 would be kinda pointless. LOL!