Several years ago I talked to the Speer reps at the SHOT Show about the differences in their brass and the fact that some appeared to have been made by another company. I was specifically referring to 357 Sig at the time, and the difference in flash hole sizes and the overall look of the head of the case. The newer cases are rounded, like they've been punched in.
They acknowledged that they had contracted out for some brass, and had also changed their production techniques, eliminating one step in the process, which is why it became economically feasible to discontinue the aluminum Blazer ammunition. The new process is what they attributed the rounded appearance of the 357 case to.
Speer, Federal and CCI are all owned by ATK, and it would make sense to produce the brass in one plant, or to at least cut down on repetition in the manufacturing process.
Hope this helps.
Fred