Well, in the first place, it's a lot of work. Or it can be. Second. you'll have to get permission to do it. It usually involves digging into the berm, then sifting the dirt through a sieve of some sort. Lots of people use hardware cloth with around a ΒΌ inch mesh. This allows the dirt to pass through leaving the lead. But this can leave holes in the berm, unless you're real careful to replace/refill the holes.
Third choice is to simply pick lead from the surface or face of the berm. Especially after a rain, a lot is exposed by wash off of dirt.
Then, when melting the recovered bullets to get the lead out, you have to be real sure they're all real dry. Never toss bullets into melted lead. Mangled jacketed bullets can retain small pockets of water, that would convert to steam in an explosion under the surface of the molten lead. It's nicknamed "a visit from the tinsel fairy". Lead will be thrown everywhere, including on bare skin!
Best bet is to start with a cold pot,(or let the lead cool til it freezes), then dump all the bullets in at once. As the whole mass heats up, the water will evaporate safely.