You used to be able to buy US savings bonds via credit card. Don't know if that is still possible, but that was a gimmick that did work.
It is a dumb idea to purchase investments with a credit card
Have a good day
Is there any reason's to not do this? You continue cycling through maxing out your credit on bullion then selling it at the end of the month to pay off your credit card bill only to buy it again. All while accruing points on your rewards card; SMART or DUMB idea?