Subsonics are a given with a suppressed rimfire. With an exception of a brick of Remington Yellow Jackets, CCI Stingers and some odd rimfire shotshells, I think I haven't even bought anything else during last 30 years. Some standard velocity ammo like CCI Standard is actually subsonic at ambient temperatures above 50°F when shot from either a <10" or a longer, pressure ported (w/ full suppression) barrel. For colder temperatures when the speed of sound is lower, slower ammo is needed. Aguila SSS is one of my all-time favorites. A heavy 60gr bullet at a mere 950fps is a great combination, providing that the barrel twist is tight enough to stabilize it. It's subsonic even at -40°F weather.