You can't utilize IRA funds to purchase and store precious metals on your own. Traditional 401(k) custodians will not let you own gold in your IRA due to IRS requirements which stipulate that the coins or bullion be in the custodian's control. This is unsurprising considering the fact that getting the physical gold could is a cumbersome process.
With a self-directed IRA, however, you can acquire gold and other precious metals as long as they fulfill IRS regulations.