Can anybody offer any information about this 7.62mm dummy machined from solid brass. Its only distinguishing feature is the knurled finish to its lower half.
The knurling comes from the lathing process. This pattern occurs if there is no center on the tip to withstand the force of the tool.
Ah…okay. Thank you. I just thought it was an unusual feature which might help identify an otherwise unmarked cartridge.
Yep, they are chatter marks.
Careless machining, the little “pip” in the middle of the base shows the parting-off tool wasn’t correctly centred. My evening-class instructor would have “had words”.
Or he is running a machine which has slop in the spindle bearings and going to centre would cause the workpiece to ride up and damage the tool (and likely scrap the part).
Given the chatter marks, I’m guessing they were not a competent machinist by any stretch of the imagination. But hey, got to start of somewhere and you can only improve from there…