re: quiet 22 rimfires -
a buddy purchased every brand and version of subsonic rimfires made, then tested them in revolvers, semi-auto pistols and rifles with barrel lengths from 16" to 24".
he then came up to my range and gave a demonstration of the best-of-the-best. after listening to each, and seeing what sort of velocities each gave, i settled on CCI 22LR 40 gr Subsonic HP #0056.
at around $7/100-rds, they're even a pretty good buy (the more you buy, the cheaper they get: available in boxes of 100, or cases of 500 or 5000)
http://www.midwayusa.com/product/266697/...ad-hollow-pointunlike short or long CB caps, these longer "long-rifle" cartridges have a heavier bullet, do not gum up the chamber, and are much more powerful. even without putting them over the chrony its easy to tell how much harder they hit the metal plates.
and in my 20" marlin lever they're quieter than any pellet rifle i've owned.
amazingly they even have enough power to fully function in the auto 10/22 rifle or beretta 87BB pistol.