The details look to be pretty evident. The brass expanded to meet the size of the chamber and it was enough to split the brass. Hopefully this happened in a well made steel .45 1911 or this could have had some really bad consequences. A .40SW is a MUCH higher pressure round than a .45ACP.
I'd amend the caution to extend to any situation where you are dealing with live rounds. You are your own worst enemy and your own best friend. Be safe everyone! =]
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