I think it may be somewhat normal, IMO.. the tip of the cartridge interruper is pretty pointed, and that has to bear the brunt of the next round getting slammed into it at full force.
That's the only point that I could find where the plastic snap caps I had were getting damaged.
Add the possibility that since mine is a 7 round mag the spring might have a higher peak pressure than a shorter mag.
I could see it getting better as the gun is broken in and the mag spring loosens a bit, and on top of that, the only problem with it dinging the rim of a round would be if you reloaded your shells repeatedly. I've seen many other guns that left thier own tell-tale "signature" on each shell and worked perfectly fine otherwise.
And my own feeling is that if I'm cycling rounds through, I'd rather have the softer, malleable metal of the rim take the ding rather than mangle the interrupter.
So the metal ones probably won't last forever, but at least they don't jam on me.
My 2 cents-