Buy no stretch of the imagination am I knowledgeable in the arena of Cristian business ethics; past or present but your skirting the constraints of Islamic finance and that would be under the mandate of the AAOIFI.
Supposition.
Defaults unlikely;most I know hold from kilo bars ---> .9999 shot. Most retail have 1oz. Eagles, Krugerrands or Maples.
If you trust scales or assay cards you're naive.
ETF/ETN +stops