I reload for my CETME. Tested some of the fired brass milsurp cases by rolling them down a slightly inclined pane of window glass. Found them to roll true...not deformed, as the longitudinal powder marks would lead you to believe! I haven't tested any American commercial cases...as those are made with softer brass, the results may be different.
The CETMEs (and G3s) are made with fluted chambers so that some of the firing gas travels down the flutes to aid in extraction...loosens the case in the chamber to minimize the possibility of torn rims and jams. If the case fire-formed to the flutes, the system wouldn't work. I full-length resize the fired cases and can't tell the difference in effort between cases fired in my CETME and smooth chambered bolt rifles.
