Shotshell Bulges

[Duffy]

I have started reloading Federal shotshells on my new MEC 600 Jr., and have a question about bulging hulls. As I reload, some shells seem to come out OK, but others wind up with bulges in the hull just above the metal base. Has anyone else experienced this, and if so, how did you fix it? Is an adjustment needed on the crimping station?

Any help/advice would be greatly appreciated. Thanks.