Melonizing is a similar process to nitriding.
The stock factory shafts are of a steel similar to a drill bit, very hard if near impossible to drill.
The MP shafts were 4130 or 4340 Moly steel, a hard steel that can be drilled; hence they were drilled & pinned as a safety measure. Presume aftermarket, Hughes etc, shafts are similar. Because this steel is softer, it will have significant wear after a while when used with a bronze bush. I used them with an alum bush...& had no wear problems.