If your budget is not very limited, Nightforce NXS 5.5-22x56 HS/ZS MOAR reticle with NF rings and 20 MOA picatinny base.
That would be a solid & bulletproof 100-1K setup for your Sendero.
I just bought a Remington Sendero 300 Win. Mag. I'm looking for recommendations for a scope, mounts and rings. I want to be able to shoot up to 1000 yards with my rifle. Please offer up your suggestions. Thanks