This is another project I just got completed. These are made from 460 S&W Mag brass trimmed down to 1.620.
Once I put in the primer, I'm pretty much going with standard data only I reduced the charge from 7.5 published data down to 7gr and according to the tester the ones he used worked just fine. For these I'm using an Aluminum 41cal gas check as an over-powder wad, and adding 200gr of #8 shot which is a 30% increase in payload compared to the factory offerings. When I got back the cases from my tester the power ring only expanded .001 from it's original size when he got them. So what that tells me is the pressures generated from my loads are real low so the 7gr of Unique is fine.
I used the same ole Notching die as I did with the 38/357 from the previous thread, and used a 40/10mm carbide sizer to size down the end of the case for clearance. I used a 44Mag sizer at first but it was just a bit to close in size of the forcing cone, so I went with a 40cal sizer which worked fine.
Again: these are intended to be used 1x because the notching creates a weak spot and the brass does split. The only way around the splitting issue is to make an over-shot card and roll crimp.