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Have you considered a 150gn Swift Sirocco II, they seem to work across the velocity range
or these, I think there is a NZ distributor
GS CUSTOM BULLETS - Specifications for use

Only out to 485 yards (long range for me) on 8 inch plates. No survivors

And here

Hornady GMX Bullets and Ammunition

VC,
Have you read this??

http://www.soarraptors.org/Documents/CopperBulletStudy.pdf

That was going to be my suggestion. The GMX were horrible in my gun, Barnes shot great gut too expensive to practises and I am not a believer in loads for this and loead for that because SURE AS GOD...

couldn't get the 120gmx to shoot well in my 6.5 mind you i didnt persevere that much

Never tried them on game, LRXs worked well on steel