Thats a Dave Corbin 22 calibre die and seating a 46.5 grain lead core into a rimfire jacket with a corbin Mity Mite press. Bit too much pressure and should have known better as I have been using that die for around fifteen to twenty years so can't complain.
If you look at the die where the threads are its a different colour and looks as though lubricant has been leaking into a crack there. I wonder if it had already started to fail there and was waiting to happen. Regards, Roly.