Re: factory prooftesting rifle strength????????
US military arsenals used to test at a peak pressure of about 65,000 to 70,000 copper units of pressure for 30 caliber and 7.62mm NATO caliber rifle and machine gun ammo. Regular service ammo had pressures in the 50,000 to 52,000 copper units of pressure. US commercial arms makers used similar loads.
The above data is based on copper crusher gages used before the newer and more accurate strain gage systems. Strain gage pressures will be higher.
Search the internet for "rifle proof loads" and you'll get a bunch of info.