If we're talking a fairly dense berm that's got a lot of lead in it, I have nver actually needed to dig at all. The layer of the top surface of the berm is almost all bullets. There is a little loose dirt there, you could scrape off the top inch or two and get mostly lead. IN an old, well established, heavily used berm, the lead builds up in clumps that get bigger and bigger right behind where most of the targets get put.
Rifle bullets have a lot less lead in them than pistol bullets, and at higher velocity they pretty much explode when they hit a solid object like a rock. For the time spent, a pistol berm will yield much more lead for much less work.
Sifters work if you have a loose sandy type soil, but here in Ohio clay they just clog up. Water works pretty well, as in a bucket with a screen in the bottom and you pan the dirt out. That's a lot of work, like I said, I just pick them up by hand and don't bother digging.