Below is a link to an article covering the 460 G&A cartridge amongst others. I do remember reading about this cartridge years ago. The concept was from Tom Siatos one of the writers in the G&A magazine.
Would be quite an effective cartridge but based on the 404 Jeffery case would not be as easy or cheap to feed as the 458 Lott which the 460G&A basically mirrors in size and performance. Looks to be a nice rifle, the customised P14 action is a good one, get rid of the white line spacer ventilated pad and it would be an interesting addition to the dangerous game rifle arsenal.

http://safaririfles.freeforums.net/thread/176