I have several IKE dollars. All weigh 25 G, except one 1977 that weighs 20 G. The red book says weight should be 24.59 G. Is this off weight enough to indicate an error in material make-up ?
5 grams off certainly is out of tolerance, sounds like one for Electron John's special machine. Where's he been lately? How does it stack up height/thickness wise to the others?
Could be a struck on Rolled Thin Planchet.. There are rolled thick and thin Planchet errors... But with a considerable difference. I want to share this webpage with you - http://www.error-ref.com/rolled-thin-planchets/
I did not want to stick my foot in my mouth because by no means am I an expert in this series. Thought thin stock but also though foreign planchet?
Considering the size of the Ike.. probably not foreign planchet. Here is an example from my collection @Mojavedave
Should be pretty easy to eliminate foreign planchet. Look at the edge. I believe we are the only country that uses the coppernickel clad copper composition. (Well Panama did too, but we struck their coins and we used the same planchets that we struck our own coins on.)