First, you need copper. Bar, plate sheet, wire or foil. Doesn't matter. This becomes the anode. Next, you need copper sulfate and sulfuric acid. This forms the electrolyte.
For bullets, you need to tumble them while plating. Just a slow tumble is all that is necessary. The tumbling drum is made from conductive metal like stainless steel mesh. This makes the circuit without having to wire up each bullet. Since the drum is the cathode, it gets plated. After a while, copper builds up on the drum's surface, reversing the electroplating current without bullets removes the copper on the drum and makes it available for plating the next batch.
There are other variables that have to be worked out. The idea is to have the copper anode inside the drum and a layer of bullets 2-3 deep in the drum so the majority of the copper plates out on the bullets. And the drum rotation is enough to completely mix the bullets.
That is how it is done.