Greetings @Rated M for Magnum.
You may find it easier to work up to a velocity rather than just adding powder and looking for pressure signs. The 6.5x55 has around 5% more powder capacity than the .260 Rem and should gain around 1% more velocity at the same pressure. The .260 Rem max loads produce about 3,000 fps with the 120 grain, 2,850 fps for the 129 or 130 grain and 2,725 fps for the 140 grain. All of these develop a little under 60.000 PSI in the .260. In my Tikka, with the exception of H4350 (AR2209) as mentioned, the velocities recorded were in line with the Hodgdon data. I also used graphs to better understand what was going on which were a great help.
Would be happy to share my notes via Email.
Regards Grandpamac.
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