What size 44 mag cast projectile?

I sighted in my 44 the other day and got nice tight groups with ppu factory ammo (240gr JHP)
It looks like that has a .4285 diameter projectile according to the wesite, though I found other sources saying .429
For cast projectiles should I go with .429 or .430? these will be going subsonic if all goes to plan.

looking at these projectiles from this trademe seller:
https://www.trademe.co.nz/Members/Li...?member=481805

Was going to go for the 260gr hollowpoint, though I see he has a 215 cup point too that may be good.
I guess the ultimate answer is to slug the rifle but I don't have any soft lead balls or casting alloy.

@Guypie

That seller is @shooternz here on our Forum.

Send him a PM he's a bloody good bloke and I'm sure will set you up with the right advise and projectiles.

Cheers
Pete