I went shooting this weekend and checked the backstop for some of my bullets and found some real wopper bullets.
They are .585 diameter all copper with six petals like a barnes X pistol bullet.
Anyone know who makes them and what weight they come in? I can only weigh 100 grains with my scale.

Took me 10 months but I finally found the answer myself .
The bullets are 12 guage barnes expander sabot slugs . I believe they are 325 grains . I wonder how fast they would go in a .585 nyati or t-rex .

real fast

Fast enough to leave a thick layer of copper in the rifling...

Remember, those bullets are made soft to expand at shotgun velocities (1000 fps down range) and might start expanding in the air if pushed at the 3000+ fps velocity possible out of a 585 nyati.

Also keep in mind that 585 dangerous game rifles will have a twist to stabilize 750 grain bullets, and would need a slower twist to shoot 325 grainers well.