War nickels, what's the deal with the variable TIDs?

[lagunabeachjoe]

I dug my first War Nickel (1945) with my Equinox 800 this past weekend.  It was deep.  9 1/2 inches deep for an exact measurement.   Also in the hole was  3 1/2 nail.  Here is the kicker.  I heard the nail with no problem but I was also getting a 19-20 hit beside it.  I dug an 1883 Indian Head the previous weekend that hit at 19-20 so that was what I was expecting this time.  No, out popped the 1945 War Nickel.  Even out of the hole it hit a solid 20.  

I have dug 4 other War Nickels this year but with the 3030 and all were around the 12-42 area.  I even sent them to a pal of mine and he also got high hits on them.  

My question is, Why do they sometime hit high and sometimes hit normally?  A 13 in the case of the Equinox and I think 12-13 on the 3030.  I normally just ignore the lower tones on the 3030 when park hunting so it is always a surprise when a nickel pop out of the hole until I see the date.  But I have found them in the past reading with the normal nickels.  

Anyone care to venture a guess on this one?  If I knew someone with an XFD analyzer, I would send them one to see just what the metallic composition is.  My best guess is that some of the original planchets of a higher silver content somehow were used and put into circulation.  But that is just a guess on my part.  I sure would like to prove it.