Through regulation he banned the import of Saiga shotguns although I think it was reversed. He’s also stopped the import of Korean War era rifles from Korea.
There are other examples but those are the two that come to mind.
Yes, I do recall a shipment of Garands being blocked, largely at the behest of collectors who didn't want to see their rifles lose value in the market flooding that would've taken place. This isn't really a ban though. You can still legally buy Garand rifles. They just cost a lot. Don't get me wrong, I have no doubt Obama would love to engage in a gun-banning frenzy if he felt it was worth the massive amount of political capitol he'd have to expend.
Honestly, I'm concerned about Romney when it comes to guns. Unlike Obama, Romney actually has a demonstrable record of signing gun-banning legislation into law. Realistically though, the gun control movement seems to be dead. Liberals learned back in '94 that enacting gun control legislation brings huge electoral consequences while having very little impact on the availability of guns or any measurable reduction in public safety. In short, it's just not worth it. We'd have to enact Britain-style confiscation measures for gun control laws to have any effect and this simply will not happen in America.
And on the subject of guns, I've been pining for a Ruger Mini-14. I don't know why. I just find them aesthetically pleasing.