I've been involved in electronics, as a hobby, for decades (early teen), and have avoid most projects involving winding coils. It's really difficult to get them wound just right, to even function, let alone get them to work right. There are quite a few things that effect the coil's operating characteristics. You could get lucky, and it works fine. May not work well. Or, could produce smoke, if the impedance is too high, and your detector tries to supply more current than it was designed for.
Really not my area of electronics, but not something I'd attempt. It's more likely to work poorly, if at all. Metal detectors are like radio equipment, and the coil needs to operate in a specific frequency range for a particular machine. Different models, brands, all use an assortment of frequencies.
