Dennis, those dovetailed bumps look excellent. I'd been toying with the idea of set in bumps at 10 o'clock and 2 o'clock on the closed bolt, under the receiver bridge and loctited set screws to centre the bolt. your's looks the far better idea.
From what I can make out, all that loose abrasive is good for is making the parts bright. Whitworth de-bunked the use of loose abrasive for making accurate surface plate and machine surfaces back in the 19th century, clearly stating that you have no control over where the stuff goes, or where it takes metal off.
Loose abrasive shouldn't really be called "lapping". Actual lapping with a series of accurate laps with embedded abrasive, and proper checking control over flatness and squareness is something completely different.
Whitworth's preference was for scraping.
I was reading an article on comparitive wear tests of scaped, periphery ground and cup ground surfaces in varying grades of cast iron and case hardened steel.
After 20,000 metres (about 12 miles) of sliding travel with proper lubrication, the least wear was between scraped surfaces, or with scraped on cup ground second.
Among the possible claims for scraped surfaces were greater flattness and better contact, retention of lubricant, and possibly locked in compressive stresses in the surface, where grinding locks in tensile stresses.
When surfaces of differing hardness were slid against each other, the harder surface suffered more wear. Irradiating the surfaces before running them, then taking radiographs after running, showed that wear particles from the hard surface embedded in the soft.
Now, what will the "gunsmithing" (bubba's garage tinkering) writers in gun magazines have to write about next month, after what you guys have said?
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