If I'm not mistaken the easiest way to determine the amount of silver in the $10 strikes is as follows:
.999 on the rim equals .60 ounces of silver
.999 on the inside (actually on the silver) equals .50 ounces of silver
If not marked .999 then just clad (except the early Hard Rock strikes) No silver at all.
I know this is not a precise measurement but I think it is pretty darn close.