sizing die for 375 super Mag

I been watching this site for quit some time now and have been collecting casting equipment. I have a Dan Wesson 375 Super Mag and jacketed bullets will be to costly to shoot. Got an RCBS 37-250 gc mold. I slugged the barrel and it comes out 375.5 what does anyone recommend sizing to. And does any one have a sizing die and an RCBS top punch number 570 they aren't using any longer?

Measure the front of the cylinder chambers (the throats), and size your boolits to that size plus .0005. And check to make sure that is LARGER than the groove diameter of your barrel.