The difference here is only .0025 per side so I think a light pass on a lathe with a boring bar would be the thing to do.  If you don't have access to one, then a vise, valve grinding compound, an electric drill and time will suffice to take out this small amount of material.  Cast 20 or so bullets, drill the bases, install a screw, then cut off the head and use them as the lap tool.  Coat the bullet with oil and apply the compound then get busy.  I bored a .429 die to .450 on a lathe with a carbide-tipped bar.  With a few passes and slow feed, it left a very smooth surface and could be used without further lapping.