I bought a selection of CB caps and sub-sonic .22 ammo and did some simple range time today. None of them would reliably cycle a semi-automatic or my full-auto. I settled on my Ruger 7722 as a test weapon, since it is bolt-action and pretty accurate. Targets were a house-cat with cross-hairs drawn on them at 30 yards. Five shot groups were fired with each variety of ammo from a bench. Control ammo was CCI Mini-mags in .22LR; covered group with a dime. Next rounds fired were Aguila Colibri .22 LR caps in . 22 LR, theses are extremely quiet, quieter than a hi-velocity through my Gemtech suppressor but the group was very erratic, at 4"...unacceptable. The Aguila Colibri have a conical bullet and do not feed well through a Ruger magazine, even bolt-action. The slug is only 20 grains and I suspect that has a lot to do with the poor performance. Next up was CCI .22 LR segmented hollow-points Subsonic. These are not nearly as quiet as the Colibri but managed a group that you can cover with a quarter through the 7722. They were as quiet as the Colibri when fired through the suppressor and would sometimes cycle on automatic through my Ciener .22 conversion in a M16, but not at all reliably and prone to tunnel. These bullets are 40 grain. They seemed to operate ok in my old 63 Winchester on semi-auto until the last round that I fired didn't eject completely and is now stuck inside my rifle in a most unusual way that will require complete dis-assembly to clear. Remington .22 LR CBs shot a slightly larger group than the CCI Subsonic rounds but were a tiny bit quieter. Still grouped around 1" with a 40 grain slug. They do not cycle reliably in any of my semi-automatics. My final choice was CCI .22 CB longs. They are nearly as quiet as the Aguila Colibri with a 40 grain slug, totally silent through the suppressor but you couldn't hear it from behind a corner without suppression. They function OK in the Ruger bolt gun and managed a 3/4" group. All rounds were fired through my Colt Woodsman with as 6" barrel, as well. The CCI Subsonic rounds would cycle reliably but are not much quieter than a standard velocity round so no advantage there. None of the other rounds would cycle reliably. I will set up the Chronograph later and get some data.