Most of my old haunts have be E-Trac'ed out so I'm digging iffy signals most of the time these days. Now this is not scientific, your results may vary and I'm not talking about war nickels. This is just an observation I've made in a trashy pulltab filled park that's kinda proven itself. So, I've noticed this trend in old nickels so I thought I'd mention it. An iffy nickel signal tends to go lower rather than higher in numbers.
If I get something bouncy in the nickel range 12-14, 11-15, 13-13, 10-13 or that sounds good or interesting, I use pinpoint to get right over it and then swing again. If it generally goes up higher on the conductive end... 16, 17, 18, 19, 20 it's probably a pulltab or scrap aluminum. If the numbers go lower, even 01-08 (conductive numbers 10 or less, but they seem to drop to 01 often) then it's usually an old nickel, but sometimes foil. Foil though will often not sound as good or solid from the get go and hovers around 03-06-ish.
So, investigating a iffy nickel signal? A drop in the CO (and FE) number seems to be a good thing. A rise in the CO signal is a negative sign. As always the only way to know for sure is to dig it up.
If I get something bouncy in the nickel range 12-14, 11-15, 13-13, 10-13 or that sounds good or interesting, I use pinpoint to get right over it and then swing again. If it generally goes up higher on the conductive end... 16, 17, 18, 19, 20 it's probably a pulltab or scrap aluminum. If the numbers go lower, even 01-08 (conductive numbers 10 or less, but they seem to drop to 01 often) then it's usually an old nickel, but sometimes foil. Foil though will often not sound as good or solid from the get go and hovers around 03-06-ish.
So, investigating a iffy nickel signal? A drop in the CO (and FE) number seems to be a good thing. A rise in the CO signal is a negative sign. As always the only way to know for sure is to dig it up.