There are a couple of ways to tell if your metal is the metal you purchased.
First you cannot weight a coin and tell if it’s real or fake. Can I prove this yes I can prove this. With Facts Laws of Science Proven and tested.
The things you need to be able to prove the your element is real.
You need an element.
You need a system that measures an element without gravity.
Elements cannot be made or destroyed Proven Fact no arguments. Every element has its own weight at the atomic level.
An US Coin pre-1965 have standards sets for element’s content. Every Coin pre- 1965 is 10%copper and 90% silver end of story. Every coin of the US currency weighs the same as a single one dollar silver coin.
If you have a $2000 you can purchase a coin ultrasound machine.
If your seller will allow you to perform an acid test. This is risky may damage a valuable coin.
My way of testing a coin to see if it’s real and my favorite is Water Displacement.
A known coin lets say 1893 S Morgan someone is selling how do I know if that’s real?
Cooper Displaces more space than Silver. In any water bottle you have lines.
You drop the coin in question into the water.
Measure the rise in water and maker the bottle.
Remove coin and repeat the process if the water does not reach the same place as the known coin it’s fake.
THIS IS HOW IT WAS DONE BEFORE LASERS!!