I'm curious what the quietest .22 ammo out there is? Specifically I'm interested in the quietest ammo out of a revolver since cycling won't be an issue but also in a semi auto, even if you have to manually cycle it.  

We occasionally have vermin that make appearances at the house.  My BB pistol doesn't cut the mustard.  I was wondering if there were ammo available that was quiet enough for dispatching vermin without causing a scene.  I live in the "semi country" so not in town but we do have one neighbor fairly close.  I figured a single action revolver could shoot .22 shorts as well buy I have no experience with them.  

No silencers so that's not an option.  What have you got for me?

https://www.aguilaammo.com/products/22-colibr-i-long-rifle-subsonic-powderless-lead-bullet

Still has a bang, but best you can do without a suppressor.

Any .22 ammo is going to be loud without a suppressor.  I'd step up to a .22 pellet gun if you want deadly and quiet enough.

Yup.

.22 pellet rifle with a 'moderator'.

My Air Venturi Avenger with the DonnyFL moderator is accurate and quiet (and a lot cheaper than the Benjamin Marauder, especially considering that the Avenger has an adjustable regulator. The Marauder Field and Target with regulator is $629 vs the Avenger regularly on sale at $299).

The pellet impact is quite a bit louder than the shot.

CCI CB long or short is going to be at least near the quietest.

Yeah, I think I'll go the pellet gun route.  At least that way on the off chance the cops do show up, there won't be any issues. Plus its a good excuse to get an air rifle which I've been wanting anyway.

Straight Colibri, already linked, is the quietest.

Super Colibri and CCI CB Caps are pretty close to each other -- I think the Super is just a touch quieter.

Accuracy wise the CB caps are way, way more consistent. The plain Colibri has so little energy that I think the
slightest variations in the barrel, fouling etc result in just crazy huge groups (group sizes of inches at 20-30 feet.)(

All are far more quite in a rifle than a pistol. Out of my 3" 317 even the Colibri has a very noticeable bang. Out of a
16" rifle the Colibri is at the level where the bullet hitting the target is about as loud as the shot itself.

OP doesn't mention what size vermin. Colibri doesn't always penetrate one side of an empty aluminum can. And the trajectory is horrible. It is quiet. I've wondered what it would sound like through a suppressor, but I don't find it very fun to shoot.

Some of the lower velocity ammo is pretty quiet out of a rifle,close to air gun quiet but handguns have a much louder report and it won’t help you much there. A rifle will do just fine with cab,cci quiet or similar and be much quieter than anything you put in a handgun

Through a suppressed handgun or rifle, I only hear the click of the hammer but accuracy is all over the place.

It's that all over the place that keeps me from shooting some through a suppressor. Not that I think Colibri could do much damage.

OP,

Any chance on switching to a .22 rifle?  If so, .22 shorts are as loud as an .22 air rifle, without a suppressor.  As mentioned, CBs are also an option & air rifle-quiet in a rifle with a 16+” barrel with more killing power.  Semi autos will be single shots, but a Marlin 39A (both of mine) feed shorts.  Not sure about Henry or others.

My personal experience with Colibris in a pistol vs red squirrels was inconsistent enough I switched to pump .22 air rifle, in addition to my police officer neighbor reminded me about laws against shooting firearms in the neighborhood.

The fuckers were destroying my tomatoes.  The red squirrels, not my neighbor cop.