Thread: 1000m rifle.... What?

Personally I would look at the 284 Winchester. Your 6.5x55 will do the closer stuff.

Very good brass available with Lapua making 6.5x284 brass. Just need resizing.
Very efficient case particularly in a longer barrel.
Get very good velocities with the 160-180gr 7mm projectiles.
Easily stay supersonic past 1000m and then some.
Easier for reloading and cheaper to run than a magnum calibre.
You don’t need a real long action or a magnum bolt face.
Comfortable to shoot without a break on a sensible weight rifle, suppressor isn’t massive though and easy to put a break on if you want.

The 280 Remington would be a close comparison.