The warding plug looks like it's "pot metal" (zinc alloy) so it was probably cast. Machining/broaching a spiral seems unlikely.

Here's an image of a much tighter twist. I don't have this lock, the image probably came from eBay many years ago:

Click image for larger version.  Name: twiskeelock-lh-450.jpg  Views: 7  Size: 20.5 KB  ID: 14045