Re: Best Long Range Caliber for Rem. Sendero
You also asked about a custom gunsmith. I use William Roscoe up in Shreveport, Louisiana based on a recommendation I got here. He runs a small operation but seems to know exactly what he is doing. Has a pretty short turn around too. Look him up on the web at LA Precision (Louisiana Precision).
He is currently working on a .243 Win project for me. He has blueprinted my M700 action, installed a Krieger barrel, and pillar bedded the action.
There are other great smiths around and maybe someone can point you toward others.