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If it helps IMR4831 is a close match for N560.

There is some data here for 160g bullets that will give you a starting point: https://shootersreference.com/reloadingdata/280-remington/

N560 would be a good starting point as would N165. I've been using N165 with good success in a 280AI for years. Other powders (N560) may bring slightly higher velocities but I'm getting 2900 fps with...