I tried this on the Reloading forum and didn't get any replies so I thought I would try it here.
I was reading that Benchmark closely duplicates the burn rate of IMR3031 with three significant differences.
1. Much finer granules (still extruded)
2. 8% more dense
3. Insensitive to temperature variations
What do you think of trying this powder in the 458WinMag or maybe the Lott? It seems that you could get enough powder in the case to give good velocity without heavily compressing. Any advice, observations, or opinions would be appreciated.

I have never heard of that powder. I'm willing to try about anything if it will help my cause. However achieving 2250 with a 500 grain bullet is no problem with several different powders using a 22" barrel in the Lott and 2300 can be realized easily in a 23 or 24" barrel. I can see no need for a faster bullet in .458 then 2300fps. To be honest 2150fps is plenty, everthing after that with a premium bullet is just "extra".

The additional velocity up to 2400 is going to add more energy but experience shows good soilds will penetrate end to end on a buffalo well under 2400fps. Over 2400fps causes intermittant problems with penetration with all but the best bullets made. That's why the Lott and several of the various Nitro express cartridges outpenetrates the 460 Weatherby mag which is going 2700fps!

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It seems there is never enough time to do things right, but always enough time to do them over

JJ,
It is made by Hodgdon. I was thinking more along the lines of achieving 2150-2200 with a 458 WinMag anf 500gr bullets. I have seen posts where Lott users have complained about velocity and it may have an application.