Took a few selected test loads to the range this morning down here in Sunny Southern Florida. Temp: 83 degrees F. My rifle is a .458 Win mag built on a L.H. Remington 700, w/21" Douglas bbl. I have a Millett Red Dot sight mounted on it. For the edification of any to whom it may concern...
These were all Barnes "triple-shock" X-bullet, solid copper hollow point. C.O.L.=2.49",Win. Large Rifle Magnum primers. Results are averages of 3 shot series:
72.0 gn. H-335: 2006 fps
74.0 gn. H-335 2036 fps
70.0 gn. IMR-3031(compressed) 2142 fps
All the above loads showed "moderate" flattening of the primers (compared to the other very mild loads I fired)with no other over-pressure indicators.
As an interesting aside....I took some 500gn. loads along that were originally loaded in 1977. 70.2 gn. IMR-3031, WW120 primer, Hornady 500 FMJ. These 30 yr. old loads turned in the following results: 2153-2103-2164-2141 for an ave: 2140 fps. No extraordinary pressure signs other than a degree of flattening of the primers.
Your results may vary....
Cheers,
Don

Thanks for the info/results don!

I am going through all of the .458wm data on the website and gathering as much as I can