Mike Morton, aged 65, joined officers for a sweep of a park in Cradley Heath.
The region's police force has drafted in volunteers to help take guns and knives off the street in a bid to tackle violent crime.
He said: "I would normally be looking for coins and artefacts which can date back centuries and reflect the history of the country.
"But it feels very satisfying to use my hobby to support the police in removing potentially dangerous weapons from society.
"I’m not only developing my own metal detecting skills but doing something which is beneficial."
If a detector does pick up trace of a dumped knife or gun it will be seized by an officer and assessed for evidence linking it to criminal activity.
Volunteers will never handle any weapons but their skills will help to seize weapons.
Jess Redmond, who oversees the recruitment of metal detectorists, added: "Our volunteers are skilled in what they do and can really help us in our efforts to trace and seize weapons.
"With the pandemic restrictions starting to lift we will hopefully be able to call on their expertise in the coming months.
"A detectorist will always be accompanied by officers when carrying out weapon searches and won’t put their safety at risk.
"But it’s a different challenge while also playing an active role in protecting communities. We’re hoping more metal detectorists will be willing to offer their support."
Any volunteers interested in helping are asked to email firstname.lastname@example.org.