Questions

[Yournamehere]

I think you mean supersonic rounds make the gun louder, as they break the sound barrier. Subsonic bullets don't and are inherently better for silenced weapons.

Also, a .22 is a poor choice for a distant kill, especially when something is attached to it that lowers it's velocity. Most of them are seen used at point blank range in movies. If I could suggest a different gun, give him a .45 of some sort. Not sure on the sound it makes, but it's subsonic, so it can't be too loud.