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Are you asking about .577 Snider, OR about .577/450 Martini-Henry cases?
I have not reformed any 24 ga into 577/450 M-H cases yet, but what I read on http://britishmilitariaforums.yuku.com/ and elsewhere suggests that you will probably crush a few before getting the hang of it.
The issue is that this is too big of a resize to do in one step.
It should be done in 2 or 3 operations.
Rather than go directly to .450, first size to maybe ~.500 then .475, then to .450
That's my experience too. I size in 3-4 stages and then do final trimming. Then anneal again. This might seem like a lot of work, but at these low pressures, the brass will last a very long time - you might not have to even neck size for a few firings.