I would suspect jeweling and this style of 'scrape' finish on the bolt body is for appearance. Aren't these treatments very thin. I'd think if metal surfaces bear against each other the pattern would rub right off.
One maker that regularly uses jeweling is Westley Richards. Over the summer on their blog, they commented about some new four bore locks, and the jist of it was about the effort it took getting the appearance right. The coverage is clearly on non bearing areas. Similar comments about their bolt rifles. It just struck me as a current example of a builder using the effect as part of their embellishment decision, rather than functional.
Steve, wouldn't machine tool ways be scraped to increase the surface area contact?
