What causes a gun to back fire?

Question

I was wondering, what causes a gun to back-fire?
And does it ever happen to modern pistols like glock 17, baretta, etc?

Back fire is when the gun blows up in the shooter's face.
It did happen to really old guns. Not sure if it ever happens to newer guns thats why I asked.

Answer 1

You can get a "backfire" when you get a double feed, this happens when the fired casing is not extracted from the breech, but the action cycles back and during the forward motion feeds another round towards the breech which is blocked by the empty casing.
Sometimes if the rear of the second round is struck, hard during this time, it discharges in the breech.
Seldom happens but is recorded to have happened.
The most logical cause for a blowback is when the barrel is fouled or blocked.

Answer 2

OK. Now I understand. The weapon explodes due to a blocked barrel or defective ammuntion.

When the primer of the cartidge is struck, is causes the powder to ignite, which creates a gas in the cartridge. The gas forces the bullet out the barrel. If something is blocking the barrel, then the gas comes out the weakest point of the weapon, which is the chamber. If the ammo is defective, the bullet can lodge in either the barrel or chamber, and cause the same thing.

Answer 3

An obstruction inside the barrel.

Fall down in the mud, don't look to make sure the barrel is clear, and BOOM

Answer 4

malconstructed bolt
using wrong /supercharged/homemade ammo
using wrong caliber of ammunition
all of these producehigher then designed pressure in the chamber and the bolt is not able to withstand the forces acting

Answer 5

The ammo is faulty. I will get back when I know more