Your two civic coppers of Isfahan are interesting :
- they are not dated but could well belong to the Qajar period
- they are of the same mint, same type and same size but with very different weights; which could indicates that they probably were not in circulation at the same time (otherwise there would have been confusion).
the copper coins had an exchange value with the official currency in cash (with a fairly stable relationship Ag/Cu ) and the weights of your coins could reflect the changes in silver standards during Qajar rule ?
For example the weight of a silver coin of 1000 dinars was 9,21 g at the beginning of the reign of Fath 'Ali and fell to 6,91 under Muhammad Shah Qajar : -25%
the difference between your two coppers : -24%
That isn't necessary this same period but that is probably the same reason....