I think Davidsons is giving bad info. Somthing does'nt jive with my info. Both , Sierra and Hornady reloading manuals indicate a ..308 bore diameter for the mini-thirty. Perhaps brand new models have .311 bore but older models do not.Too us Reloaders of this fine cartridge, it would be of intrest to know serial #s as to the larger diameters introduction. It was my understanding that bullet makers tried to cover both bore diameters with the .310 bullet. Bottom line, slug your bore before handloading for the mini-thirty!!