My preferred method of collecting scrap is to visit the range a couple of days after a heavy rain. The scrap is exposed as the water has washed a lot of the dirt/soil away. I then rake lightly with a leaf rake to dislodge the exposed bullets/boolits and scoop them up. The soil here is a clay or clay loam with heavy clay content, so amount of dirt raked up is minimal. I then sift through a 1/4" screen to get rid of the small pieces of dirt and hand pick out the large pieces. The pieces of dirt and rock that are about the same size as the bullets/boolits get removed from the pot when I render the scrap down to ingots. Collected about 150 lbs in 20-30 minutes last time I went to the range, including the rough cleanup with sifter. No digging at all. But you have to time it right so that you aren't getting sticky clay or the berms have been shot.
Anyway, that's how I've done it. About the least labor intensive method I've come up with. Of course, there are only a handful of days a year that meet those conditions.