Replica Prop Assistance (Metal Casting With PlatSil Silicone Molds?)

Is it possible to cast metal pieces and or full props like swords and the such with a PlatSil Platinum silicone mold?

I don't know specifics about that brand, but you will have a very hard time finding a silicone rubber that can handle any molten metal harder than lead or may be pewter. Metal pieces are most easily made by casting the piece in wax, then shell casting it into metal in a foundry.

If you're looking for an alternative to real metal foundry work, cold casting metal is fun and a bit easier than pouring molten metal. I've used the smooth on nickel silver powder with smooth cast 325 and it gives the piece a hefty weight and a metallic real metallic finish.

There's multiple tutorials on the Smooth On site for cold casting metals, here's one of them:
Metal Cold Casting More Realistic Than Ever! | Mold Making and Casting Materials Rubber, Plastic, Lifecasting, and More

There are a number of high temperature RTV casting silicons available via the internet , and I've used plenty, in casting hot metal parts mainly pewter and zinc over the years, so casting a sword is possible - but you'd need quite a bit of silicon I'd estimate four or five kilos as you'd need quite a thick mold to stop the hot metal distorting as you pour, so a hardwood brace frame should be used, a large foundry pot to cast from , a good open space to work in , and follow all the safety precautions for handling and casting hot metal , protective clothing , leather aprons, gloves, masks etc you want no distractions as any spillage would be potentially very dangerous , so if you attempt this take great care.

regardless, if you plan on casting anything out of metal, make sure to do so using proper protection as any moisture will have a reaction to the molten metal = small explosion = metal on skin = ouch = scars. I always suggest casting small parts in melted crayon as to somewhat learn the technique or working with hot molten type materials. Its quick easy and cheap as opposed to trial and error with any form of metal. In the end if your looking for something like a sword to mold and cast, I highly suggest looking at foundries to do the work for you.