AC,
In addition and also in relation to sample size, is a coin lying flat, at a particular depth, isn't going to prove much of anything. What about all the coins that are edged, or completely on edge? What about the various depths?, etc.
Then of course, regardless of methodology, is confirmation bias. I WANT to believe!!! lol
There is also denial bias.
"So, for you hunters who claim you can accomplish such a thing with tones, ID, or the Deus II X/Y screen, or the Manti's Target Trace, I'm calling BS"
"Well, to be blunt, I claim those hunters are delusional, and also maintain a good dose of confirmation bias."
I am the kind of person that tries to keep an open mind and a neutral stance.
However, I will research and use any possible advantage that might help me to differentiate between targets that have a regular shape, meaning they are in the same shape as when they were produced, they have different compositions but they have similar target IDs and audio pitches depending on the tone setting being used.
Learning those target's inherent characteristic responses when they are on the surface to medium depth for me anyway, may help to lessen the "randomness" of my ability to distinguish them.
Since I live in a very large US city, I simply can't dig it all for every reason that you can think of in a public park. I don't consider myself to be delusional or full of BS when I search for any discernible characteristic that might help.
In the case of the Manticore using All Terrain General, the question about undamaged aluminum screw caps and as stated by the OP, US copper pennies, I use the 5 tone setting and move the 4th to 5th tone break high enough (76 works for me most of the time) so that most of the medium sized screw caps stay in the 4th tone bin. Even most of the flattened ones do too. Since I am going to cherry pick/dig any target that appears to be coin/jewerly sized that has a tone above that tone break at 76 anyway, I'm fine with digging any larger or messed up aluminum screw cap that high tones. At least for me there aren't that many to deal with compared to the ones that land below 76.
Other search modes and settings adjustments may produce something different on the Manticore.......I just haven't explored this yet.
As far as the smaller shot bottle aluminum screw caps and US zinc pennies or big gold rings......good luck. I dig these a lot. I can't even classify a US zinc penny as a repeatable shaped target anymore. When they are heavily destroyed like the one in the photo, the target IDs are way off. They are already pretty variable even on zinc pennies in good shape on SMF VLFs with wider target ID ranges.
I consider myself to be a beginner on the Manticore like most of us should. It is a very different detector from the Equinox and from the earlier Minelab SMFs.
I have found that lowering the sensitivity to between 16 and 20 gives the Manticore a better chance of having stable target IDs on these targets if they are shallow to medium depth from surface 4 to 6" deep. However, where I most often detect, target IDs are very relative much deeper than 6" deep due to mineralization and soil moisture. So a deeper screw cap can have a much higher target ID on the Manticore and on other SMF VLFs.