Aguila Colibri

Aguila Colibri is a brand of "quiet" .22LR cartridge, a light bullet propelled by only the primer.  I'd considered these for indoor use, but the lead in the primers would be an issue.  Comments on forums seem to indicate that penetration is an issue, especially at practical distances.  Sounds like a Super Colibri out of an 18" barrel is the best of the two for velocity and penetration without excessive noise.