One is probably the 1st issue brass version... the other may be a later "bi-metal" version.

And don't hold me to the "bi-metal" description - there has been discussion on this and I only mean it is the lighter/ less brass composition variety.

If you can weigh them on a gem scale, the brass version weighs a few grams more than the later issue.

The Hyatt $2.50's have the same deal... only one is reeded which is an easier "give-away" on which variety one have.