Is it possible to open a precious metal 401k or IRA and fund with per tax funds

Regarding a 401(k): the investment options offered in your 401(k) are up to your employer. It's possible they might offer a mutual fund that invests in precious metals, but I don't believe diect investments in precious metals are art of any 401(k).

Regarding a direct investment in precious metals as part of our own IRA: it's possible, but must be handled very carefully or you risk losing the tax sheltered aspect of the account. In general you can't just buy the precious metals and hold them yourself, but rather must use an agent to handle it for you . Do a web search on "precious metals IRA" and you'll find lots of companies selling their services in this regard.

As an aside - without debating the merits of investing in precious metals, assuming that you have a well balanced investment portfolio I would advise that investments in commodities should be held in your taxable account, because of the favorable tax treatment that is already available for long term capital gains. Put investments that generate income (dividends, interest) in your tax-advantaged accounts such as your IRA and 401(k). This would include taxable bonds and high dividend stocks.