Don't pick them up. Shoot more. Never need to buy more gravel. Larry
Was at the Lake Christine shooting range in Basalt, Colorado and in front of the 8 rifle benches the ground was several inches think with spent 22, and handgun brass. Lots of steel cased 7.62x39 cases also. Not a sign of gravel for several feet in front of the benches.
Our little range is getting littered with rimfire hulls.
On a side note, I pick up all my brass when I shoot in the woods. However, when hunting I leave the brass where it lays for future archeologist to find and try to solve the puzzle. Years ago, I harvested a bison using an original Sharps carbine in 50-70 Government. I used a factory cartridge loaded in the 1870-80's. I left the brass where it laid. The harvest was in historical bison country. Someone someday might find the brass and rightfully believe it was used to take a bison. However, it was 130 years after the evidence would suggest.