1999 Nickel Real?

I don't have a scale precise enough, but it is non-magnetic, and by size just in between a nickel and a penny. It is definitely heavier than a penny, closer to a nickel in weight.

When I put the nickel on top of another nickel (the same date), this nickel is a little smaller at it's widest, about 20mm instead of 21.2, while a penny is 19.05, just a touch smaller.

The metal is definitely as heavy as the nickel, but it is much thinner.
About the thickness of a penny, but the metal is nickel or something non-metalic. I figure it weighs between 3.5 to 4.2g.

I've heard of pennies that were used by mistake to make a few nickels, but this is definitely not penny colored anywhere, it looks and feels more like the weight and feel of a nickel. I know nickels were made with 75% copper and 25% nickel that year.

What happened to it I'm very qurious about. I've tried looking for matching foreign planchettes but can't find anything. Does anyone know of a foreign planchette matching this? (about 20mm, 4g, and pennyish thick (give or take a tiny bit))?

After all of your very valued comments, I decided to try and measure the coin with the Celestron (Both a 1999 Regular Nickel and this coin).
All the measurements were taken 5-6 times to make sure I wasn't too far off.

Both coins came out at 19.4 at the widest flat. The other side was 18.5 mm for the odd one.
The regular thick was .21 and the other was .18mm

Does this still make it a partial collar? (It'll be my first find for this kind of coin and I'm still learning). I thank you for all your help.

Time for the microscale purchase. Should be here within a week. I was using the popsicle stick trick for the different pennies but this needs a little better.