How does the firearm work?

If you have ever shot a bullet, you have harnessed the power of hot, expanding gases.
In every firearm, a propellent (such as the black powder invented by the Chinese as early as the ninth century) is nestled against a projectile in the confined space of the barrel.
Once ignited, the powder creates superheated gases whose molecules burst apart against a projectile, blowing it out against the firearm's muzzle with great force and velocity.
Early firearms like cannon and muskets were loaded through a muzzle, with powder and bullet or ball inserted separately.
In most modern firearms, a cartridge is loaded into a chamber at the back of the barrel.
The cartridge contains bullet and powder, as well as a primer that ignites when struck by a trigger-released hammer.
The technology has been refined over the centuries but the principle remains the same.