I just can't visualize the cutting of the neck with a broach. Maybe by
forcing a male to impress the lines... Any case, brilliant.

My son has the HK21, the beltfed version of the G3
https://en.wikipedia.org/wiki/Heckler_%26_Koch_HK21

The fluting is shiney and polished, can't have been EDMed. My guess is
its pressed in, just like rifling buttons do it.

The HK21 brass is not reloadable, IMHO. But we did buy a whole gaylord
pallet of surplus military 7.62 brass so we'll be good for a while.

Karl