Okay, so imagine you have a toy that shoots a little ball when you push a button. When you push the button, the toy springs into action and shoots the ball out. But when the ball hits something, it bounces back a little bit because of something called "recoil."
Blowback works kind of like that, but with guns. When someone fires a gun, the bullet shoots out of the barrel with a lot of force. But at the same time, the gun itself recoils backward a little bit because of the force of the explosion that propels the bullet.
Now, here's where forensics come in. When a gun is fired, there's not just the force of the bullet shooting out of the barrel that needs to be accounted for. There's also the force of the gun recoiling backward. And since the gun is often held by a person when it's fired, that person's body will experience that recoil force too.
So, if a gun is fired and the shooter is very close to a wall or some other surface, there might be evidence of that recoil force on the surface. This evidence is called "blowback."
Blowback can take different forms depending on the type of gun and the ammunition used, but it might include things like gunpowder residue, bullet fragments, or even tiny pieces of skin or clothing from the shooter. Forensic analysts can use blowback to help determine things like the direction a gun was fired from, or how far away the shooter was from the surface where the blowback was found.
In short, blowback is a way that forensic analysts can gather evidence from the recoil force of a gun after it's been fired. It's like a little clue that helps investigators piece together what happened during a crime.