Haven't loaded much for the 260 as I am a big fan of the 6.5x55 but here goes for general and free advice which is worth exactly what you paid for it.
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1. Check the reloading manuals.
2. Seating depth does not have that much affect on pressure until the bullet is jammed in the lands.
3. It is really not that long as 2.85" is standard for many short actions like the rem. 700
"When you disarm the people, you commence to offend them and show that you distrust them either through cowardice or lack of confidence, and both of these opinions generate hatred." Niccolo Machiavelli
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