Hi Rich, I guess for a better term, it most likely swages its way thru the bore? As I see absolutely no provisions for chip clearance... Just an excellent example of brute force overcoming resistance?.... I've seen sharp tools cut several thousands effortlessly, and by the same token, seen a .001" or .002" upset hold tons of force?...
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As for the button rifling process, It looks insanely easy to do.... but, also, not cost effective as a cheap "button" is going to be a couple of hundred all by it's self... I'm challenged enough with just threading the tenon...
... Best to you Rich, til....lat'r....GT......
