como hunter: I hunted an old Drive in theatre several years ago with an M-6 started with 6 by 10 DD coil, very trashy, having about the same experience you describe. Changed to the 4 by 6 coil also a DD, incredible difference, in less than an hour I had a pouch full of Quarters, dimes, nickles,and pennies, most at 2 inches or less. Another hour, another full pouch. I was nearly whipped by this time. On the way out I stopped in the play ground area under the screen, got a hit that read dime 5 inches, dug the signal, up came a 1916 mercury dime in very good condition face up, I sat for several minutes afraid to turn it over,wondering if I would have a heart attack if it had a D mint mark, it didn't. Found out later that the drive in had been built on an old farm site. I hunted less than one twentieth of the theatre,hoping to get back by next spring. Slowing my swing speed, reducing sensitivity, and putting on the small coil worked.