I've loaded the 458 & the 460.
The 460 with 110g of 4350 & a 500g bullet duplicates the factory trajectory at 100 yds. so I was very satisfied.
I've loaded a 600g Barnes in it - forgot the powder charge but it DEFINITELY gets your attention off hand in the recoil department!
I have the 505 Gibbs but I've stuck with factory ammo bought years ago.
I wasn't quite ready to commit to custom dies at the time.