I hunted around a site last weekend that had colonial, civil war, and modern trash. I still get fooled occasionally by a deep bent nail or flat piece of ration can but by far the worst is digging 22 bullets and shotgun shells. Sometimes a scoop of dirt off the top will let you know if it's iron or a deep good target but to me the sounds are very easy to figure out. The guy I was hunting with has an arsenal of detectors and was using an f75 ltd, which is what I used before the GPX and never another VLF again, he had me sweep a target and it blew my ears off, I said modern trash and it was deep piece of aluminum. I then had him sweep a strong signal and he couldn't hear it and it was a really deep and old shotgun shell. I found a seated half dime, two V nickels, and a colonial tombac button amongst all the trash and I never hunt coins but I could almost coin shoot with this thing. Sweep your targets, if they sound good then pump the coil over them as sometimes they'll break up indicating iron. Occasionally shallow bullets will break up a little but the sound of lead is a long sweet ringing noise that's hard to miss. Make a test garden with everything imaginable and you'll learn the sounds everything makes in no time. If every relic hunters knew what gpx hunters knew the VLF market would be hurting except for coins shooters.