steve white,
I swage .318 bullets, myself, usually from .321" 170gr 32 Win. Spec., but some from .323" Herter bullets. I didn't have any problems with them, but never tried them at 250 yds. I try to keep the difference in diameter to .005" or less, and .323" to .318" is precisely that. I don't have experience with Buffalo Arms bullets, but they have a good reputation and I don't think you will have a problem with them.
Mike