Detector worked for me when I had my own backyard range but that was quite a few years back. Now, wouldn't work worth doodle-squat on our club range. Members, for the most part, are pretty good about policing up brass from the concrete firing lines but tend to let whatever drops in the surrounding gravel and grass lay where it falls. Club bought a pull-behind job-site magnet for the JD we use for mowing...collected something over 200# of steel-case .223/5.56, 7.62x39, and 9mm the first time they ran it over the grounds (we've six open multi-use bays, an 8-station conventional pistol line, and two rifle lines: 100 and 300-yard)...and that didn't include the grass areas areas around the rifle lines inaccessible to the tractor. Yesterday morning, during a 'cease-fire' for changing targets, I raked a couple hundred fresh, once-fired Federal .223s from the slope in front of my bench on the 300-yard line...don't shoot/reload the caliber so they went into the recycle bin.
Bill