It's on a bolt action Savage Mark II. Just shot some 22's I had on hand not any sub sonic.
I've got a Mark II myself, get you some CCI's 710 fps. Without ear protection all you will hear is the firing pin and after a second or two you might hear the bullet hit the target. It's a lot of fun with friends and the kiddo's love it.
Stay below 1,100 fps and you'll stay subsonic for the most part. CCI Standards are 1070 fps, so depending on temperature and elevation they will be subsonic. If you go with 1,050's or lower you'll pretty much always be subsonic.
In pistols, due to their shorter barrels, will shoot High Velocity's subsonic. I only shoot bulk ammo in my pistols to not waste my subsonic's. I've no idea if Stingers stay subsonic in pistol barrels.
I use them with a few different .22 rifles to shoot pigs at our lease in GA by shooting them in the ear at no more than 50ish yards. A deer would have to be standing very close to hear it, so after shooting them you can leave it lay or drag it behind you and keep hunting.