At a match today, my wife went to slide lock with her 320 Legion. She reloaded to a MecGar 21 round magazine with a Taran +2 extension. This caused a serious malfunction, that ultimately made the pistol into a single shot, with her having to force the slide back into battery after every successive shot. At the safe table, after finishing the stage, it was clear the ejector was bent up by inserting the full magazine, and that was preventing the slide from moving back into battery without assistance. This is what it looks like.
140mm magazines are necessary for USPSA CO competition, but I would not want to use an extended magazine for carry that allows vigorous contact with the ejector.