From what I read this happened to an individual who worked at Sarco (gun parts) in New Jersey. It did happen during the summer and Sarco did have some details on their site. I do not remember the exact details.
I've seen a modern 45-70 that I am 99+% certain was not overloaded with a ruptured barrel. Rember, Berthelot used a powder similar to this in some of his experiments with pressure waves in and out of phase in the late 19th and early 20th century.
I found some information by searching at the Accurate Reloading Forums.
I don't know if the information was correct but it mentioned Unique as one of the powders used.
I have shot hundreds of .45/70 loads with this powder. I view all cases for the correct charge before seating a bullet. The rifles I use Unique in are not antiques either.
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