Geraldton detectives say a loaded gun, gel blaster and assorted rounds of ammunition were among items seized by police in a search warrant.
Detective Senior Sergeant Bruce McDonald said officers raided a home in the Geraldton suburb of Glenfield.
He said the search uncovered a haul of items believed to be linked to illegal drug activity.
A 54-year-old man has been charged with 15 firearm and drug related offences.
"The homemade handgun was located loaded, which posed a critical risk to attending police who executed the search warrant," Senior Sergeant McDonald said.
"We will allege the person charged had possession of the home-made handgun to protect himself from what we will allege was illicit drug activity."
Police said the home-made handgun was capable of firing 12-guage shotgun rounds.
Senior Sergeant McDonald said there had been an increase in homemade weapons uncovered of late.
"There has been a few [firearms] located and seized lately which concerns us," he said.
"Not only do they pose a significant risk to the community, but they can also be a danger to the person who uses them.
"They are normally constructed in clandestine environments using unreliable and untested materials."
Detectives said a quantity of methylamphetamine, MDMA and cannabis was also found during the search.
