Recently got a .22 can - all the "standard" velocity ammo (often advertised as target ammo) , and even some of the high velocity cheap bulk packs (got an occassional crack), has been subsonic in a 18" tube - at least here in PA in the summer, since it varies by environmental conditions. Also used the Aguila ammo that is branded as subsonic (not the SSS) and it was perhaps a hair slower than standard, but not much. It all cycled just dandy.
Edit: whoops, just realized I think you meant the powderless rounds (i.e., CB caps, etc.) and not subsonic. The muzzle blast on anything simply labeled as "standard" or "subsonic" will still be quite loud, unsupressed. The CB caps and similar don't have a chance of cycling a semi, and some don't recommend use in a rifle, since the bullet may not have enough energy to clear the bore.