I have a 2000D nickel that is only 4.3 grams and regular is 5.0 grams. Is this a flaw from the mint? You can see some small spots of what looks like copper showing as well
No it eats away the surface fairly evenly so it keeps the detail as it gets thinner and thinner. You can get coins down to near paper thinness and still have decent detail.
When you swallow a coin and then retrieve it.. digestive acids will take that much off, patina is a tad more dark..
Here's an example of an acid treated coin I own. Details pretty much still there, but the coin is much smaller. This one was likely used in a candy machine to make it think it was a dime.
Have you tried sticking a nickel in "Coca-Cola"? I have. Nothing happened. However, I'm am inclinced to go buy the biggest bottle of Coke that I can find and see if I can cram a nickel down its throat, recap it and keep it in the fridge for a week. The last experiment was in a glass on the counter.
I was just guessing on the Coke. It does eat up pennies though. I have tried that. Nickel is probably too hard.
I've got nothing on your underweight nickel...maybe get another scale. I used to live near Puyallup though!