I specialize in dropping tiny sight/scope mount plug screws. Then, when I use my heavy magnet to find them, I get every filing and chip I ever knocked off a piece of iron or steel, plus enough paper clips to start a new office, but not THE screw.... If I'm lucky, I find the screw I lost the last time I mounted a scope, but of course that's another size!
I may soon be stuck with shooting only .22s because all my scopes are missing a screw or so, and may not hold against the recoil of the .361 SuperiorMag! (Actually the only magnum rifle I own is a .22WRM. But the other barrel IS chambered for the awesome 3" mag .410!).