I recently borrowed an older Radio Shack model detector from my dad to see if a metal detector would do what I needed it for. I target practice in my back yard quite a bit and I like to pick up as many spent ammo casings as I can find. I thought a metal detector would be a good way to find the ones hidden in the grass. I use steel and brass cased ammo. The detector I borrowed does not seem to detect the casings. Actually, it seems to detect only certain metal pieces. There are two adjustment knobs, one labeled discriminator and one for volume. There is a switch for meter/battery test. These are the only 3 controls on the detector. Is it possible this is a model that won't detect the ammo casings, or am I doing something wrong? Are there any inexpensive detectors that would serve my purpose?