Considering the condition which looks like environmental, if the other side is as bad, then it could have lost weight from whatever it came in contact with, like acid or something harsh that ate away at the surface. Copper/bronze is soft and easily susceptible to environmental substances affecting it. So, to answer your question, it is not normal. Normal is around 3.11 grams.
No. Die deterioration doubling or worthless doubling.Wexler's Coins and Die Varieties (doubleddie.com) http://www.lincolncentforum.com/die-deterioration-doubling-ddd/
@Nathan Kristan, none of your coins are doubled or errors. The 1960 has been in circulation and worn down so that's why it weighs a bit less. This 1986 has a chance at a DDO, but pictures are blurry and it is likely a plating issue, or DDD.
