Since the mint STOPPED using full copper based planchets in 1982, yes it would be, to say the least, "uncommon" for a 1991 cent to weigh 3.11 grams as it should weigh 2.5 grams as all copper plated, zinc core cents do (at least at some point in their lifetime). 1952 – 1982 is 95% Copper and 5% Tin & Zinc; 3.11 grams 1982 – Current is 97.5% Zinc and 2.5% Copper; 2.5 grams One problem with the latest composition is it corrodes quickly. That corrosion (and any other gunk) can add weight, although most of the time it gets light. Of course, you get other oddities of posters who claim their cent was struck on a canadian cent. But 2014 -2020 Canadian cents .. that's another story. Also, we get many people who use the wrong type of scale to weigh their coin. Jewelry scales are mandatory to 2 or 3 decimal places. Other food type scales round to the nearest whole number, which thus can be 1/2 gram off an actual weight (and also are not designed to be as accurate thus are off from that error rate too). So 2.5g ends up 3g, 3.11g ends up 3g; 2.49g can end up 2g or 3g. And of course pictures are mandatory, and so is a picture of a weight measurement on a jewelry scale.
People weigh their zinc coins on a 500 pound grocery scale, it comes up as 3 grams, and then they list it here as 3.11. Yes such a coin is possible, but you'll have to show photos on a proper scale, perhaps your coin is a 1981? Perhaps your scale is not calibrated properly. Take some other coins that you know are 2.5 and 3.1 and test them. Photos are always welcome and easy to upload.
It's a scale that weighs hundredths o.oo g. The penny is like brand new I will post a picture. It's accurate I've put dollar bills on it an it weighs exactly one gram...
OK cool. Anxious to see it. Some later date coins have been discovered on copper planchets, so it's possible. On the brand new aspect, usually that's copper plating on a zinc cent. A 30 year old copper cent will be darker and more chocolate looking. Good luck.
And when I put it on my index finger and flick it in the air then catch it... You can hear a strong ring or chime the entirety of the time it's airborne
Right now Im not home but I do have the penny I'll snap a pic with my phone (low quality) as soon as I get home I'll take quality pics on scale.
This has nothing to do with determining the metal content. Some phone photos are OK. But if it is blurry don't bother to post them. I doubt it is a doubled die. If it is a copper planchet the doubling wouldn't matter anyway. Most forms of doubling are not valuable.
Easier to bunk or debunk something if it is visible. I will reserve judgment until then. What is the latest known off metal cent? 1989? Any from the 90's?
I'll hold off until I can get quality photos. I apologise for posting without pics. I think you'll be quite surprised.
I recall reading about a 1986 off metal and a 1989. But I welcome any confirmation/ debunkings of that. Stack's Bowers sold a 1989-D struck on a Pre-1983 cent planchet in MS 62 BN for $22,325 in February of 2014. Mike Byers claims to have sold a 1990-D: https://mikebyers.com/13961052.html