Concave or Slightly Cupped US-PI coins?

IloiloKano

Has any other collector of US-PI issues noticed a significant number of these coins seem to be cupped? I have seen several examples covering various denominations and dates. The latest instance I noted was a 1911s Peso where the coin slightly bulges from the center on the obverse, and it is slightly depressed on the reverse. There is no noticeable mark on the coin that would account for this slight but even and radially symetrical bend. If anyone else has noticed this and would like to share your speculation as to the cause, I would appreciate information regarding your own observations and experiences. I wonder if it may somehow may result from the change to 75% silver alloy in 1907. If it is not a product of some natural environmental or alloy chemistry effect, then why do I see so many examples? It is difficult to produce an image that conveys what I am trying to describe, so I am left with only the hope I have clearly described the nature of these coins.

Rickc300

I have no idea on how, but I mentioned this back in 1999 on another forum, I am hoping to hear more from the more experienced collectors/dealers in this field. I never did hear any response to my original question regarding the way these coins look. This is really out of my field, I have knowledge of "roller" dies from some of the German states that I collect, but nothing that accounts for this...

Rick