A homemade shotgun or Tumbera or bakakuk is a firearm made with practically no money and with unsophisticated articles like nails, steel pipes, wooden pieces, bits of string, etc. It can be made by "low budget" criminals and is sometimes found in jails.
The common design of a homemade shotgun is: One curved steel pipe, a piece of wood with a nail in the centre and a longer steel pipe with a smaller diameter than the curved one. The piece of wood goes inside the curved pipe with the nail pointing to the tip of the pipe, then the other pipe is put inside the curved one the nail makes as a trigger.
A 12-gauge shotgun shell is placed inside the longer pipe, then the long pipe is placed into the curved pipe and pulled to detonate the shell.
See films such as Sin Nombre and Celda 211 to see one in use.