Maybe some of the folks that are cranking out these faked error coins are actually using a micrometer. Besides, due to the fairly small size of a Cent, some differences would be fairly unnoticeable without the use of a micro-micrometer. No, not all coins done this way are missing the Copper plating. The many folks that have made these coins usually to make money, have pretty much tried this on every denomination including pre-1959 Copper cents. They continue to do so as along as they can continue to fool folks.
I am sure that the information is out there on how to do this to a coin. However, I have no reason to look for it as I buy, sell and collect error and variety coins and other coins as well and would not try this or even sell one of these coins to one of my customers! When it comes to U.S. coinage, you can pretty much do what you want to them as long as you don't try to melt down the Copper cents and try to sell them to a Recycler. I wonder why the U.S. Treasury never made a similar designation for Silver U.S. coinage. It is hard to fathom how many Semi-Key and Key Date Silver coins have been destroyed during the Silver and Gold craze plus common date coins are now less available and should be more rare but no one has any numbers on how many of any of the coins of specific Dates and Mints are still out there.
Frank