if you take a pop bottle of various sizes and fill it with something soft like cotton balls ect. and place it over the end of a .22 cal. rifle it will act as a silencer

This one ought to be right up JDShootists street.

i recall seeing a guy use an empty pop bottle as a silencer on c.s.i a while ago, i think they said something about escaping gases, or something like that, but i doubt that any silencing effect would be very substantial.

Would that make it a "pop" gun?

If you examine the sound made by firing a pistol, it is made up of several components. In a supersonic round, (ie 9mm, or .357 Magnum,) the highest decibels are created by the "crack" of the bullet's supersonic boom. Although loud, it doesn't sound much like a gun going off. The simple way to get round this, is to use a subsonic round, such as .45 ACP. It is possible to get subsonic 9mm as well - downloaded to go slower than the speed of sound.

The quietest, (lowest decibel,) component of the sound is the mechanical component, as the various parts of the gun move. Automatic pistols are usually noisier, because the entire slide reciprocates on firing. You can't do much to muffle this, but it is usually inaudible much above 50 feet away, and also doesn't sound much like a gun.

The part of the sound we all identify with gunfire is the sharp roar, or "bark" of the propellant gases escaping from the barrel - and this is the part silencers work on, allowing the gases to expand and slow down, in a confined space, making them much quieter. The silencers, (strictly speaking, supressors,) we are all used to are a metal tube, of significantly greater diameter than the barrel, fitted to the muzzle. They generally have baffles inside, like a car exhaust, with holes drilled in the middle just big enough for the bullet to pass through, and more holes round the edges to provide a suitably tortuous route for the escaping gases to follow. They are often packed, in between the baffles, with steel wool, to further retard the flow of gases, which is why they are only good for a few shots before they need to be re-packed, as the steel wool compresses. Supressors do not work on revolvers - there is a gap between the cylinder and the barrel through which gas escapes - thus a supressor on the barrel simply forces more gases out of this gap, making plenty of noise!

In actual fact, I can speak from actual experience when I tell you that the "two-litre soda-bottle silencer" is actually very effective. When used with subsonic ammunition, the expansion chamber provided by the bottle has a significant effect on the noise - remember that, unlike a normal silencer, the bullet doesn't have an existing hole to pass through in the base of the bottle - in the split second it takes for the bullet to travel the length of the bottle, and punch a hole in the base, the gases following it expand considerably in the bottle and are travelling much more slowly when they exit through the newly-made hole. It is not as effective as a proper commercial silencer, but inside a building, or from across the street, most people would not readily identify the sound such a weapon makes as a gunshot. I have fired such a weapon on an indoor range, and many people who were there, (experienced shooters, all,) thought I'd had a misfire, or a "squib load," and didn't recognise it as a shot fired. (Incidentally, the cotton wool balls are a largely unneccesary addition and potentially destroy the accuracy of the shot.)

Interestingly, I have also seen the episode of CSI mentioned: only one problem; in the TV show, the culprit fired two shots - but the "soda-bottle-silencer" is strictly a one-shot device - on the second shot, there's a big hole in the end of the bottle and it's supressing effect would be very limited - but in the show, the two shots were equally quiet!

Incidentally, I've just noticed that the original post referred to a .22 rifle - most .22 ammo is supersonic, so the effect of a supressor is minimal. What it does mean, however, is that, although everybody can hear the shot, very few will be able to identify where it comes from - the principle sound component is the crack of the supersonic bullet passing through the air - a sound which is generated from an infinite number of points along a linear path, not from a single point source. Some military snipers use supressors on rifles, for exactly this reason - you know you've been shot at, but not by whom!

Subsonic .22 is available, for rabbiting and vermin control, but is pretty useless for anything else, due to it's inherant lack of power - a good thick sheepskin coat is actually bulletproof against it! And .22 is pretty much the only rifle calibre available in subsonic loadings.

inkeeping with the improvised suppressor theme, heard of potato silencers JD?

apparently, holding a potato infront of your pistol barrel will dramatically reduce your gunshot sound.

i think its a load of bull, on the expanding gas stuff, and i dont see a potato helping much.

Sorry, Mikisan, potato supressors are actually some of the most effective "Heath Robinson" devices you can use. Anything which slows down and supresses the escaping gases will have some effect in making the shot quieter, even the common-or-garden pillow. The reason a large potato, into which the barrel is firmly pushed, then held in place with a gloved hand, works so well, is that the potato doesn't just slow down the escaping propellant gas, it actually absorbs a significant proportion of it into the cellular structure of the vegetable! It will even work with some supersonic ammo, since penetrating the potato slows the bullet down slightly as well, potentially making it, just, subsonic. Once again, strictly a single-shot device, however - the potato is usually quite "mashed" after use!
I'll tell you a true story - in 30's New York, an assasin walked in to a restaurant where a well-known local mobster was eating. Everybody thought he was just making a delivery to the restaurant, singe he was carrying a large box of fruit, with a spectacular watermelon in pride of place on the top. What nobody knew was that there was a model 1905 Colt's Pistol, in .45 calibre, hidden in the box, with its muzzle jammed about 2 inches into the watermelon. Needless to say, he shot the mobster. What's wierd, though, is that there were some 40+ witnesses in the restraunt, not one of whom tried to stop the "delivery man," from leaving, because not one of them actually realised any shot had been fired! Reportedly, the only noise anyone heard was the squishy thud from the watermelon, which they thought had just been dropped, or otherwise damaged - because the action of the gun was so firmly embedded in the melon, it prevented the action from cycling, so there wasn't even any mechanical noise! (.45 ACP is subsonic, of course.) So, vegetables, fruit.... you'd be surprised what does work!