I invested in silver and gold for quite some time. While these prices will fluctuate, gold will always be a standard of wealth. The government makes trading/selling it quite troublesome. Taxing is even more hard to wrap your head around.
Bottom line is commodities like ammunition, weapons, food, water, and tools are much more valuable in a time of trouble, not metals. If you are investing to make money, metals are just fine. If you are buying to prepare for collapse, there are much more functional and valuable "supplies" as I mentioned above.