Usually I am very good with errors and varieties, but this one stumped me. I bought it because it looked cool for $2 at my coin show, just listed as a Panama 1 centavo, doing research, its supposed to be made out of bronze! This Im pretty sure is silver,it sounds like it when dropped and tones blueish. The normal coin should weigh 3.10g and this one weighs 3.05g. Whats going on here? I think it could be an off metal error, if so, whats it struck on? So many questions...
The weight of your coin is within tolerance, so it's not an off metal or wrong planchet. I'm certain it's been plated as a novelty item.
Bad plating jobs are relatively easy to spot, but it's not obvious from your pics. I am leaning towards plating as well. One way to tell if it's plated is to look at all of the surfaces, paying particular attention to the rims and edges. There may be small areas where the coin was in contact with a clip or other fixture and the plating is missing. You may also see bubbles or the beginning of corrosion underneath the plating if the coin wasn't cleaned properly. You should also measure the density. The main reason I think it was plated is that assuming the coin is the correct size and thickness, the weight would likely be different it it was made from a diff alloy. Silver is denser than bronze so there is no way it could be within 0.05 gms in weight
If it was struck in silver and of the correct size it would weigh close to 3.6 grams. Since this coin is slightly underweight, but within tolerance it is almost certainly plated.
Let's think about this. If it is the correct size (measure it), if it were silver it would be 3.6 g and if it bronze it should be 3.10 g. You say it weighs 3.05 g, so it can't be silver if it is the correct size.
If it weren't plated it would be worth almost $2 in that condition. https://www.ngccoin.com/price-guide/world/panama-centesimo-km-22-1961-1987-cuid-1081294-duid-1536739 Panama coins are equal in value to US coins with most of them the same size and weight so as to fit in each countries vending machines, tolls, parking meters interchangeably. I don't know if the US minted those Panama coins, but if it were on a silver planchet if would be a few years before 1967 and the coin would be smaller. It could be "wrong stock" as you say, but then there would be a couple dozen of these beauties in circulation. A quick scan on Google doesn't turn up any other examples. That doesn't mean it doesn't exist. Just saying.
