Isn’t all Berdan primed ammunition “mil-spec”?
While it is generally assumed that Berdan primed ammunition is “harder”. This is not necessarily the case—both Berdan and Boxer primers come are available in “hard” and “soft” varieties. Boxer primers (invented by Col. Edward Boxer, a British Army officer) are generally used in US-made ammunition—these are generally “softer”. However, at least one US manufacturer, CCI, makes “mil-spec” Boxer primers. Unfortunately, CCI doesn’t manufacture 7.62x39mm ammunition. Berdan primers (invented by Col. Hiram Berdan, an American US Army Ordnance officer) are generally used in Europe.