I thought it was superseded by the .495 A-Square. I think that's the one I'd pick. As far as I know, they are both based on the .460 Weatherby necked up. The 500 has a .450 Rigby type shoulder and the .495 doesn't. Both fire .51 600gr bullets, the .495 at about 2250fps and the .500 at about 2400fps. IIRC Wieland wrote favourably about them in his dangerous game rifles book, but preferred the .495. I don't know if the 500 is a slightly longer case whereas the .494 can fit any action suitable for the .458 Lott.