Thanks for the load data. It gives a starting point for planning. I'm still looking for H4895 starting data.
This may be old news by now, but BARNES new manual Number 4 shows 68.5 grains of H335 as a starting load for the 450 TSX in the 458 Win. Max is 72.5.
In my experience (in a long-throated Ruger #1 in 45-70 and my CZ550 in 458 Win), H335 is just a tad slower than H4895 in those two big bores. 1 grain less of H4895 (67.5 grains) would be a very safe starting point IME. Hornady's manual seems to confirm that with their 500-grainer. Personally, I prefer H335 to H4895 as the powder is compressed less being a ball powder and Hornady recommends it as the top choice for both the 458 Win and the Lott.
Interestingly, Barnes also seems to prefer that powder over H4895 as it is listed as giving best velocities, or second best, with all their bullets recommended for the 458 Win. H4895 is not even listed for the 458 Win in the Barnes new manual.
