If you have a mold already but casts a smaller size like .314 etc you can beagle it like the Americans do .
Basically you but some adhesive heat resistant aluminum foil and place a carefully cut out strip on each face of the mold so the mold is essentially bigger . Then just cast away and measure and resize if necessary.
It does work as I used to do it on martini Henry dies to cast them at .470 etc
If you cannot locate the foil I can send you some down but it is easy to source . Worth a try