I tend to shoot lead only out of my Diamondback. Mainly I am trying to avoid the wear of copper bullets vs. lead. I once read that the life space of the barrel with copper bullets could be measured in the 10's of thousands of rounds, while lead was basically infinite.
I could be wrong, but I don't believe that shooting copper bullets through your Diamondback will shorten the barrel life that significantly. I read an article a couple of years ago where someone put over 100,000 rounds through a Glock 17 and the accuracy of the pistol was not affected at all. What affects the accuracy is not so much the friction of the bullet on the bore but rather the effect of the hot gases from the burning powder.
My opinion is accuracy is most impacted by poor cleaning techniques and storage, but that is my thoughts.
Look at it this way, glocks are still made, diamondbacks are not. I would venture to guess that my diamondback has the most rounds down it of any one I have heard of. At 45,000+ rounds (I did not look up the exact number) I figure that maybe I might have some clue as to the problems that might happen and be able to compare my diamondback to others I have seen. Thus the insight I offered.