I once used a hand held metal detector to find led shot in some teal that were killed with illegal shot. There was however more than just one piece of shot in the fully feathered ducks.
Most metal detectors will pick up both ferrous and no ferrous metals. You need to asked when you buy one.I have had some tungsten pellets (TSS) that a magnet will not pick up, they are pure tungsten and weigh the same as the pellets the magnet does pick up
would there be an issue with these if used as waterfowl shot?( if not magnetic), a pair of pliers won't begin to leave a mark on them let alone deform them.
I have a Garret Pro-Pointer AT which is fantastic, but at a cost of $125. You can get the Chinese versions for $20, and fellow metal detectors say they work fine as a back-up.A Garrett "carrot" is a very popular handheld. Don't buy the Chinese fake though.