Barack Obama might seem an unlikely investor in the firearms industry. But the president, a fierce advocate for gun regulation, has money in a pension fund that holds a tiny stake in gun and ammunition companies.Although Obama’s stake is minuscule, worth no more than $30, it reflects a much larger surge of investment in the industry — some it by unwitting investors.The president is among millions of Americans buying into gun companies as mutual funds have increased such holdings to record levels, according to a Reuters analysis of institutional investment in firearms companies.Since Obama took office in 2009, mutual funds have raised their stakes to about $510 million from $30 million in the two largest gun manufacturers with publicly traded shares, Smith & Wesson Corp and Sturm, Ruger & Co.