I was having trouble with RTV High Temperature Silicone Mould Making Kit. With some left over liquid Pewter - I poured it into a PLA mold and it did not just melt. With this in mind I have experimented....
After some work I now have got this as a workable method for producing metal objects. Given my past hacks - Traffic light cufflinks - Hackaday as proof I made some Hackaday Cufflinks.
Source files are at Youmagine - https://www.youmagine.com/designs/had-cufflink-mould and Tinkercad https://tinkercad.com/things/9erQIt3o35j Assuming you have a 3D-Printer, if you invest a few pounds for a ebay-toaster-oven and some lead-free Pewter make you own HaD Cufflinks.
Tip etc are in the videos.