The old ZIP case used a .22 blank to propel a very light bullet, more of a copper as I recall. The ZIP company may have made adapters to fire regular .22 bullets too, I guess.
But I know that in my old American Rifleman magazines, I've seen ads for the ZIP auxiliary cartridge that used a .22 blank to shoot its very light proprietary bullet. This was used for indoor practice, and perhaps dispatching very small varmints like rats, mice and sparrows. Not sure how accurate the system was, I've only seen the ads.