Why do Indian Head pennies read differently?

[olddigger]

Variety 3 (1864-1909) IH pennies read lower and/or disc out lower than wheat & memorial cents on most if not all detectors. The Var. 3 IH and Lincoln wheat cent have the same composition (.950 copper, .050 tin & zinc), weigh the same (3.11 grams), and have the same 19 mm diameter.
The above applies for dug and non-dug coins.
Does anyone know the technical reason for the difference?

[joecoin]

The only possible explanation I have come across so far is this. The 5% of the alloy that was composed of tin and zinc had the proportions of those two metals set at the discretion of the Mint Director. Perhaps the proportion of tin to zinc was different between the two coin types.


One other thought crossed my mind, the striking pressure could have been different, resulting in differing electrical signatures.

[olddigger]

Good point, I hadn't thought of the percentage difference of the tin and zinc. The percentages would have remained the same over a 45 year period. Perhaps someone at the US mint know's what the exact percentages were.

I had consider stamp pressure as a reason and perhaps because of the bolder relief that IHs appear to have.

Thanks

[Rudy]

Olddigger, the difference is simply because they are different.

Indian head coins struck between 1859 and 1864 contained 88% copper and 12% nickel, as required by law.

In 1864, the alloy changed to 95% copper and 5% tin and zinc, and the weight of the coins was reduced from 72 grains to 48 grains.

Why the change in composition? Mint research in 1863 had indicated that bronze was an excellent alloy for minor coins, and so the copper-nickel alloy was discontinued. Another possible contributing factor for the change was the whitish color of the early cents, which combined with their size was enough to confuse many merchants into thinking they were dimes.