For a "beanfield" caliber (and I assume deer?) I'd look as calibers like 25-06, 270,7mm and the good ole 30-06. Not very exotic or "custom" but if we're gonna stay with factory ammo that takes advantage of a long action I think those are solid choices. Most the others that come to mind are either short action or not very available. Hairtrigger has good advice. Shop around. I'd look at it as a prime oppurtunity to get your feet wet with reloading. Yeah, there's some start up cost....but your building a custom gun. Consider part of a package deal. Then I might go with 270 Ackley Improved just spice things up a bit
