Head space on the 308 is a touch longer.
The older gun might have had enough slop worked in the allow the 308 to “fit”. The new gun was too tight for the slightly longer 308.
On the new rifle, the commercial brass had swollen into the flutes of the chamber. I had to punch the brass out with a cleaning rod. CETMES roller lock like an HK, and the flutes let the gas by to help open the action.
http://www.thefirearmblog.com/blog/2013/04/30/beware-commercial-308-fluted-chambers/