Experience, one of my favorite aspects of the hobby is to locate the shoreline areas that are defunct children's summer camps. Many of these are now converted to private campgrounds, or have been sold and developed. I have a boat so that I can gain access to these locations from the water, therefore I don't need anybody's permission to cross their land. But I only hunt these areas during the off season, although legally I can hunt right up on someone's front lawn if it falls within what the State considers the "high water mark". But I'm not going to act like an idiot and be a nuisance to people paying high mortgages & taxes by detecting next to their dock in July.
So back to the matter at hand, most of these children's summer camps had .22 cal rifle programs, and some appear to have had skeet shooting over the water courses. I also end up with a good amount of musket balls, lead pistol slugs & brass, plus all manner of rifle cartridges and slugs. The higher caliber stuff usually comes from areas where old hunting camps & lodges were located on the shore. Also Boy & Girl Scout camps have all sorts of buttons, badges, pins, barrettes etc. that are copper or brass based.
Now with the above information, having used a variety of detectors over the years at different frequencies. And......with the X-terras which present a unique opportunity, that being the ability to change to three different frequencies on the same detector using the same style coil, provides a means to do direct comparisons on the "same" platform. So within my nappy little head I've had the different responses versus frequency coalesce. These aren't "air test" opinions, it's thousands of dug targets in the field.
And now for an unpaid political opinion. Even though I hate digging .22 cal cartridges & slugs, Lord knows I've dug thousands, when it came time to select a summer camp for my kids, any camp without an archery & riflery program was scratched off of the list. Archery & riflery impart knowledge, teach discipline, respect, and provide immediate feedback(bullseye) by following good instruction and technique. The discipline & patience I learned in NRA shooting programs as a youth have stood me in good stead, especially in the hobby of metal detecting. End political opinion here.
HH
BarnacleBill