are you saying the diameter is not as important as the weight? my coin is 26.95 gram. how do you know whether it is counterfeit or not?
The best way to know if a coin is made with coin silver is to measure the density of the coin. The density (Specific Gravity) of any item is found by dividing the weight of the item by the volume of the coin. The result is a number that compares the density of the object to water. (Water = 1.00). Coin silver (about 90% pure) has a density 10.31 times heavier than water.
If the coin is made of copper the density will be 8.90.
It is possible to form an alloy with a density equal to silver. But while it is possible to create such alloys most of the alternative alloys do not possess the same properties as silver. So the ring test should be performed.
This is all high school level science - nothing that should defeat any of us.
My book on Counterfeit Portrait 8Rs is available from Amazon http://ccfgo.com/TheUnrealReales
or from me directly if you want it signed.