I tried several mags, as I have a variety. The CZ 18 round mags with springer base pads worked fine. The Mecgar 19 round failed (but worked fine in my friends shadow). Stock CZ 18 round magazine with base pad I got with the gun failed.
Very odd the 18's failed, the 19's are known to not usually pass. What rear sight are you running? Could've tried squishing it down if you are running an adjustable.