8 round mags have a tendency to have the 1st round dip down and catch on the feed ramp. I bet with 7 in the same mag it does not do this. We've crammed 8 rds. into where 7 were designed to go and in some clips/guns this does not work well. Many will not use 8 rounders for carry. The Novak and Tripp mags address this by using a slightly extended mag. The Chip McCormick is also slightly longer than a stock flush 7 rounder. If you gun will run 100% with 7 rounders or 7 in an 8 rounder I would not worry about it. I would not start working on the gun yet.