That .4335" groove diameter is within spec. SAAMI specs a larger groove diameter for .44 mag rifle vs. .44 mag pistol.
For bullet options, I've had good luck with an old Lee group buy mold. It drops at .434" and I size them to .433". Strangely, I still have good accuracy in my pre-safety .44 mag Rossi with .431" commercial cast. My own .430" sized bullets aren't quite as accurate, but still pretty good considering my barrel slugs .432" if I remember right.