When I got my Century CETME, (mine also has a C prefix on its serial number) I had heard great things about its reliability, so I went out and sought some of the crappiest-looking surplus 7.62 NATO ammo to put through it I could find.
I found a guy at a gun show that was selling a bunch of damaged stuff (dented rounds, bent rounds, etc. A lot of this stuff had headstamps in what appeared to be Hebrew, and a few rounds of the infamous TZ 80 was also represented. A lot of it looked like it came right out of belts and were likely misfeeds from a MG.) which he was selling for components and I picked up a hundred or so of them and tried running them through my rifle.
Most of them fed, fired, and extracted just fine. The only real problems I had was with seriously bent rounds. Those that were only mildly bent, the rifle was able to 'iron out'.
Based upon my experience with this ammo, the CETME is ONE HECKUVA RELIABLE RIFLE, and in this regard needs to concede NOTHING to the AK series.
I have never tried commercial ammunition in my CETME. Just about everything I feed my CETME are reloads in NATO cases using 147 grain FMJ, or the 162 grain .30-06 AP bullets, ahead of Ball C-2 powder. With this stuff, never a stutter.
EDIT: Thinking back now, I can remember TWO problems I had very early on. Neither was the rifle's fault.
One of the used 1960's dated aluminum W. German surplus magazines I picked up for it broke its follower spring (it rusted through). The springs in the German magazines are made with awfully small gauge wire.
I wasn't out much, though. I paid $3.00 apiece for those mags, and the other ones are fine internally.
I also had a feed lip problem with a steel CETME mag I bought (again, secondhand surplus) that depressed the bullet points enough on one side of the magazine that the bullet would catch on the front of the magazine box when the bolt tried pushing it out. I got this magazine to work by using a pair of pliers to bend the front of the lip up and out a bit. I then painted the outside of its feed lips yellow, so I could identify it in the future. This mag has never given me another problem and works just fine, now.
Apart from these solely magazine issues, NOTHING wrong with the CETME.