260rem

Good luck on your hunt. It will be interesting to see how the brennecke slugs work and what sort of shots. Good idea to have the backup too. An extra big bore or two in reserve never goes astray when one is so close to a big beast as they don't always run away from the shooter to die.

I'm intrigued too, with the 'modified .50 BMG cases'.

Good luck on your hunt and looking forward to hearing about it. Please take some photos. Should be fun.