Most reports are that they are so similar they're interchangeable, but in the cartridges I've tried, I can never get as much velocity out of the H4350 before pressure gets too high--seems spikier.
Availability issues had my trying AA4350, and that might be my new favorite. It seems very similar to IMR, but meters much nicer. Not exactly your chambering, but I last used it in a 25 Souper with 100 grain SMK's, and I just kept adding powder, and it kept producing nice groups at 200. My bottles also indicate it's made in Canada, might be fairly available to you.
