I guess I don't understand... as I see it, for brass to split longitudinally and not start at the case mouth, two things have to be present:
1) the brass has to be hard and has to have lost its ability to spring back. For this reason, it makes sense that nickel is going to split quicker than brass.
2) there has to be sufficient room in the chamber to allow the brass to expand past its ductility point. This actually relates to #1, above...
I have been loading and shooting since 1980, and the only cases I have ever had split were 38 Special cases that were shot in an old M&P that was originally a 38 S&W. Cogswell and Harrison had re-chambered the revolver to 38 Special, and as we all know, 38 S&W brass is larger in diameter than 38 Special. The resulting chambers were large enough to split every 38 Special round fired in the revolver.
Now, having said all that, I sincerely think either the chambers in that revolver have been beaten out and stretched by too many hot loads, or that particular cylinder is soft and has stretched.
In short, I don't think the brass is to blame; at least not completely.
If I am completely out to lunch, someone please re-calibrate me. I am never too old to learn...