Example: I want to buy the house and the furniture, lock stock and barrel.
Origin: This phrase refers to the three primary components of a firearm.
"Lock" is an archaic term for what is now called the "action" or the "receiver". It was originally called the "lock" because the mechanism locked the hammer back in the cocked position. The trigger releases the lock to fire the weapon.
Stock is the portion of the firearm that the holds all the other parts together and provides a grip for the shooter. This is the part of the firearm that was traditionally made of wood.
Barrel is of course the metal tube that the bullet is fired through.
If you purchase a gun "lock, stock and barrel" you got the whole gun, complete. Dating back to the American Revolutionary War, this refers to the three essential components of a gun (the lock was the firing mechanism).