Latest estimates have the amount of guns in the US at over 310 million. Yes you read that correctly, 310 MILLION.
And therein lies the problem, they will NEVER get rid of all guns and buy-back schemes etc are fine but the reality is the 'bad guys' are unlikely to willingly hand them in as well as a significant amount of the population that believe strongly in the 2nd amendment. Remember, this was written to provide security against government tyranny so any move by the government to remove that will be portrayed as the government trying to silence the masses (while clearly this application has changed greatly in the past several hundred years).
As MBT mentioned, there are a LOT of people dying in places like Chicago - I think I read somewhere that the weekend before the Oregon shootings there were 49 shootings in Chicago with over 20+ deaths. And Chicago has some of the strictest gun laws in the US.
Really the short of it is that they need to start properly enforcing the gun laws that exist and then try to find a way to get as many guns off the street as possible.
Frankly, I'm quite amazed that there aren't MORE shootings given that there are almost as many guns as there are people in this country. And all the comparisons to the UK and AUS etc are fine but, using the worlds most trustworthy source Wikipedia, there are 6.6 guns per 100 persons in the UK, 15 per 100 persons in AUS and 112 per 100 persons in the US so to compare 'advanced countries' is a fairly simplistic view of it.