Is it possible to actually catch a bullet in your teeth? Or would that just ruin your mouth?
Most handgun cartridges can still punch through a thin layer of steel. Your teeth wouldn’t do much. The bullet would pass through your mouth striking the brain stem. It wouldn’t just ruin your mouth, it would kill you.
This is also a popular magic trick, so let’s explain that. You have the magician, and their assistant. One of them has a pistol loaded with blanks. Sometimes it’s a starter pistol, but really could be whatever. A particularly ambitious magician could have a live round loaded to demonstrate that, “no, really, it’s a real gun,” though this creates a very real risk of a catastrophic failure.
If you see them load the bullet, they’ll probably use a dummy round for safety. This will look like a live bullet, but without powder or primer, so it’s effectively, “safe,” if an error occurs. They’ll palm the dummy replacing it with a blank during the loading process. This is slight of hand, but that’s about as tricky as this illusion gets.
At some point, the magician will conceal a bullet in their mouth. Under the tongue or in the cheek will work, and it can stay there for awhile. If they’re smart, they won’t actually use a lead round. Lead poisoning is not a joke, and if this is a standard part of their act, it can result in health issues later in life.
The assistant will stand at least 2 to 3 meters from the magician, aim for their mouth and fire. The magician will then produce the bullet placing it between their teeth before opening their mouth to reveal the bullet they’ve, “caught.”
Because you’re dealing with a blank cartridge, this is an act where you really do not want an audience volunteer for your assistant. That is still an option, but the magician can still be seriously injured by powder burns if the blank is fired too close to them.
Catching a bullet with your hand is a very similar illusion. You simply palm the bullet in your hand when you load the blank, and then reveal it at the appropriate prompt.
So, there’s your explanation for how professional magicians do this. Please don’t try it at home, because if anything goes wrong, the results are catastrophic.