What that means plus the why, when, and how of doing it
Running a suppressor “wet” means adding a liquid, gel, or grease to the inside of it. When the hot combustion gasses hit the liquid (which we call an ablative medium or just “ablative” when used in this context), it evaporates. This rapidly cools down the gasses, which can make a big difference in sound suppression! It makes a suppressor as quiet as it can possibly be. As an added benefit, it typically eliminates muzzle flash as well.
Choice of ablative medium is relatively wide open, but the most common options are water, petroleum jelly, wire pulling gel, and ultrasound gel.
First, a warning! Do not add too much of any ablative, and do not shoot a suppressor wet if it isn’t rated for it. Adding too much ablative can increase pressures inside of the suppressor, causing catastrophic failure. So…follow the manufacturer’s instructions and don’t go overboard.
Water, of course, is the simplest to source and it’s also the easiest and cleanest to use. Just a capful or so inside of a suppressor will reduce the sound volume level of a couple or a few gunshots fairly dramatically. Downsides to water include the fact that it leaks out of the suppressor very easily and its effect diminishes very quickly.
Ultrasound gel (widely available on Amazon and elsewhere) is a great alternative. It’s thicker than water so it’s more likely to stay in place inside of your suppressor rather than leaking right out. It lasts for at least twice as many shots as water does but, like water, it doesn’t leave behind any residue inside of your suppressor. It’s safe, it’s clean, it’s very effective. Pro tip: ultrasound gel can often be added to a suppressor without having to disassemble it. Simply squeeze a “worm” of ultrasound gel out of the tube/bottle and lower it vertically down into the suppressor’s bore before tipping the suppressor over to the side, allowing the ultrasound gel to fall down into the baffles. It’s quick and easy, and it’s also generally the correct amount of gel to use.
Petroleum jelly (e.g. Vaseline) is a top choice when you need the ablative to stay where you put it. A small amount can be applied inside of each baffle prior to assembling your JK 105, 155, or 195 series suppressor, and it won’t leak out. This is a great option for a CCX suppressor, for instance, that you’re going to conceal carry but want to shoot wet for maximum sound suppression. Pro tip: a small piece of electrical tape applied over the bore of the end cap will prevent any potential leakage. Petroleum jelly and wire pulling gel are the thickest, heaviest recommended options so they last the longest – at least 3x as many shots as water. The downside, however, is that they’re messier, more difficult to apply, and don’t burn out of the suppressor as cleanly as water and ultrasound gel do.
In order of effectiveness, water is the winner precisely because of how incredibly rapidly it vaporizes. That fast evaporation cools the combustion gasses more quickly and more thoroughly. Ultrasound gel comes in at a very close second place, even though its effect lasts substantially longer. Finally, the heavy greases like petroleum jelly and wire pulling gel have slightly less of a sound suppression effect, but because they vaporize more slowly their effect also lasts for many more rounds and it will stay in place inside of your silencer while you’re hunting or concealed carrying.