My understanding of the idea behind the pre-etch was that it brought the metals to two different levels. Subsequent wet carding would then be more aggressive on the higher level, more or less skipping over the lower. I don't care for the premise, as it seems to indicate a very strong etching and a tectured finish when done. I didn't pay much attention after coming to that conclusion, so I'm not certain on the rest, but I believe that the normal etching process was followed beyond the first, heavy, pre-etch.
As I said, no experience with that process,but I've seen guns that were, to my mind, too heavily etched. I simply didn't care for the result. The procedures I'm following leave a smooth surface.