Unique Strikes On Different Composition Planchets

@rec, you are asking a whole bunch of questions so I'll tackle one or two. Different metal alloys have different densities, so even when the planchets are the same size, they will weigh different amounts. Knowing that wear, holes, aftermarket plating and other indignities will change the weight of a coin, I think that getting an accurate measurement of the mass is a good first step.

Off-metals most often occur when the planchet from one coin series is accidentally fed into the press of another coin series and struck. Common examples of this include quarters on nickel planchets, halves struck on quarter planchets, or nickels struck on cent planchets. In such examples, the planchet will be both the weight and metal content of a "normal" example for the respective planchet it is struck on. For example, if it is a nickel on a cent planchet, the coin will be the correct weight for a cent at 3.1 grams and contain the copper alloy for a cent.

There are a number of off-metal types, with some including transitional off-metals (struck in the correct series but on the prior year's planchet that is of a different metal or weight) such as the 1943 cent; reverse transitionals (struck on the next year's planchet, which is of a different metal or weight); struck on a foreign planchet (struck on the planchet for a foreign coin); or struck on an unknown planchet (this simply means the planchet cannot be identified). Off-metals are known for most series of U.S. coins and with many world coins. A good example of a transitional is the 1943 Lincoln Cent struck on a copper planchet (likely from 1942), instead of the normal zinc-coated steel planchet for that year. It also is the incorrect planchet for a 1943 cent, with a weight of 3.1 grams instead of the weight of a steel planchet - 2.7 grams. Both the metal and weight are off in that case, although the "denomination" of planchet it is struck on (a cent) is the same. Coin experts speculate that they were struck by accident when copper-alloy 1-cent blanks remained in the press hopper when production began on the new steel pennies.

Struck on a foreign planchet can happen when a planchet intended for a foreign nation's coinage is struck by dies for a United States coin. This type of error was more common before 1984, when the U. S. Mint cut back its production of coins for other countries. What is less commonly known is that it still may occur as planchets are supplied to our mints at times by commercial vendors, and these vendors also service the mints of other countries. So it's not impossible for a shipment of planchets intended for one country to accidentally include those of another country. Even currently the Mint makes blanks for: Nickels, Dimes, Quarters, Half dollars, Dollars but for pennies, numismatic coins, and bullion coins, the Mint buys blanks. https://www.usmint.gov/learn/produc...n-production

I also have mentioned a case where a strip of copper (for cent planchets) was mistakenly run through the planchet cutting machine when it was set for dime planchets. Thus copper dime-sized planchets were made https://coins.ha.com/itm/a/1271-5871.s