It's super easy to get rid of the bottlecaps. Just put it in all metal, bring the good sounding target to edge of coil and you will hear change in tone and see numbers jump.   Hand on heart, I did a test in my garden and asked a mate to hide 20 coins and 20 bottlecaps......i came outside with the Nox, did my little trick with all metal and out of the 20 targets that i thought were coins i was right on 19 out of 20. 19 coins 1 bottlecap.   Simple.   Or