I picked up an idea from an old guy at the proving grounds,
He simply took a canvas tarp (OD Green, go figure) to the side of the bench, let it drop down and connected the other side to poles between bench stations.
The brass hit the tarp, rolled to the bottom.
I went one step farther, I cut a hole in the bottom and slid a bucket under it.
You have to shake the tarp when you are done, but everything falls into the bucket.
The local range rolls out heavy construction plastic, has it on a rounded edge 4x4 with a hand crank & universal joint on the end of the 4x4 they use to roll it back up quickly.
Keeps people from tearing up the grass when it's wet & they have a shoot.
They just leave it rolled up when they aren't needing to extend the firing line.
As for fishing brass out of grass, did the idea of running a weed eater before you shoot cross your mind?
I'm sure the range wouldn't complain if someone helped with grounds keeping!
I started with chip gravel... The weeds tried to take over, so I salted the ground.
15 years later I wish I would have got a few sheets of tin and laid them down before the gravel so weeds didn't march on me in force... Like my grandpa used to do with tin sheets, tin cans, etc before he laid a path or drive.
The old guys had it figured out, but they didn't throw anything away, it all found a use.
Underlayment would keep my salt & gravel where I put it...