Remington or CCI CB 22 long. Not the Remington subsonics. They are louder then the cb 22 long . The CB 22 long travel approx 700 fps and the Remington subsonics travel approx 800-900 fps. You can check them out on the Remington website. The CB 22 long will not function a semi auto action, keep that in mind
You need .22 ammo that contains no powder; the bullet is launched by the powder of the primer compound only. Cheaper Than Dirt sells the ones I use down here to whack the pacas that raid the vege patch (love grilled paca). They caution against using them in long guns but my short-barrel Marlin does fine with them as does my .22 pistol. Cheaper Than Dirt.com
Do not buy Long Rifle .22's. You need CCI's CB LONG .22's. Not Long Rifle. Totally different .22's. They are every bit as quiet as a pellet gun if not quieter. Here is a pic of them. No other i have found can compare to these and that includes all shorts i have tested. They won't work most auto bolts so they are best used in single shots or lever action rifles. I use my Marlin 39A. Cabelas sells them as well as Bass Pro. As far as i know, nobody else makes .22 Long shells but CCI.
CCI CB Longs. 700+ FPS and a 29 grain pill. Twice the energy of a normal 22 pellet gun. Midway-USA also carries them. Quiet in a closed breach 22 rifle. The longer the barrel, the quieter they seem to be. They don't cycle any of the semi-autos I've tried them in. Some of the subsonic rounds work alright, but make more noise than the CB Longs.
I use CCI .22 shorts through my 24" M61 and it is very quiet, on par with my 5mm pellet rifle. My approach to a silencer is to fire the rifle from inside the bathroom - window open just enough ..... The loudest noise outside the house is the vermin getting hit.
Keep in mind that there is a downside to firing .22 shorts and longs in a gun chambered for Long Rifle. After awhile the powder residue will build up and prevent Long Rifle cases from chambering until after a proper cleaning with a brush and solvent. Lead will also begin to build up, making cleanout a chore.
CCI makes CB Longs, and CB Shorts. Both run at 710 FPS and are identiacal in every way except the length of the case. One is a log rifle case and the other is a short case. Both are pushing the same bullet and both only use the priming charge.
CB longs will not foul a Long rifle chamber as they go in just as far as a LR.
During the "rid raccons" thread all of this was discussed in excrusiating detail and I went out and bought every kind of ammo talked about.
The CCI stuff is by far the best.
I had one round, the Aguila 525 fps CB cap which was very quiet but would only penetrate a 2x4 about to the base of the bullet. All of my pellet guns will out do that so nothing good there.
CCI is the best for sure. the longer the barrel the quieter it is.
That was my entire .02 on this subject. Been there done that, never even got to shoot a ****! But I'm well stocked on .22 ammo