Sizing .458's down to .440" would be a daunting task in the first place & require VERY heavy machinery capable of standing much pressure, especially for heavily jacketed ones.

Bumping bullets up would be easier, require expensive dies, but there are not many jacketed .429's of sufficient weight - as in none I am aware of - 300gr. is about it.

Cast is the only way I can see and 2,000fps to perhaps 2,200fps is about perfect maximum. Then, there is the mould problem.?????

Old WW's of the crimp-on variety, made of lead, Antimony with some minor % of arsenic(needed for hardening), cast, then heated in an oven 10F below "slump" temperature, then quenched in cool water will, after a period of 12 hours attain maximum hardness of about brinel 33/34 and can be driven at ANY velocity as long as a good enough lube is used. I have done this with 275gr. .375's and driven them to 2,700fps with 1 1/2" accuracy at 100yards.
The really cool thing about these hardened WW bullets, is they are not brittle.