Bonanza is correct, you can load a 458 Lott to 2500 FPS with a max load of IMR-4320 and a 26 inch barrel, the next grain up got me a slightly sticky bolt in that gun so I cut back about 3 grs. to 84 grs. of IMR-4320 for 2350 FPS. I wanted to see how far I could stretch that string, and how far my expected velocity of 2300 FPS was from absolute max...

I learned the 458 Lott can really utilize a long tube as I couldn't even come close with a latter Lott with 22' barrel....and understand that barrels can differ as much as a 100 FPS from one to another, so perhaps not every Lott with a 26" tube will do this...I also learned the Lott at that velocity would make your teeth ache...