By the time you insure, maintain, repair, index for inflation, securely store, deal with poor liquidity come sale time etc a non-income producing "asset" will need to work pretty hard to beat conventional investments.
Guns of most sorts make crappy investments.
If you know your field really well, and you know the market, sometimes you'll turn up some really good buys, or you'll get in on the ground floor of a field that takes off. Don't count on it to make you a lot of money though.
RG