Thanks Gian-luca!
I'm slightly hesitant to give away exactly how I make the Type 16s, because it took a lot of trial and error and conversations with people like Hector Cole (who was also very hesitant to give away his trade secrets!) to work out how to do it, but essentially the barbed section is made separately from the socket, and both pieces are attached in the forging process to become one solid head.
There are other methods, for instance rolling the socket and extruding a wide flat spade shape where the point would normally be, then splitting it down the middle and folding it back on itself to make two barbs, but the original technique as shown in numerous x-rays of extant heads show that the two-piece method is the historically correct one.