45-90 is not the best basic case because base diameter is under 12,8mm and the base diameter for the 11,2x60 is 13,00 mm like the mother case 11,15x60R Mauser 71.

absolut best basic case for this round is the 458 Win Mag but any other of this belted cases will work as well. I have got a lot of 300 once fired 300 Win mag cases and need two days to form this into 11,2x60 Schüler.
24 differents steps and lost less the 10 of the 300 but if you buy brass I recommand 458 Win Mag.