The closest I could find to 70 percent was from this post from ABC News, 6/26/08 By Gary Langer. To round 67 percent favored banning assault weapons to 70 percent favor banning semi-automatic weapons and then taking it out of context where the majority don't think that will work is certainly hypocritical since the news media is always out to catch the politicians for being misleading. From the abc site:
Consider an ABC News poll on the subject last year: Six in 10 favored "stricter gun control laws." But just 38 percent favored banning the sale of handguns, and 42 percent favored a ban on carrying concealed weapons. By contrast, 67 percent favored banning assault weapons and 55 percent favored banning semi-automatic handguns. In previous ABC/Post polling, support has been broader still for mandatory registration and licensing for handgun owners, background checks and trigger locks. And after the Virginia Tech shootings, eight in 10 backed a national registry meant to keep guns out of the hands of the mentally ill.
Views of the Second Amendment are one factor informing attitudes on gun control; there are others. One is some skepticism about whether legislation would do the job; while six in 10 support stricter gun laws in general, fewer, 49 percent, think such laws in fact would reduce gun violence. Instead better enforcement is preferred to new legislation, by 52 to 29 percent.
And perhaps most fundamentally, far more people blame gun violence on the influences of upbringing and culture than on access to firearms. In our 2007 poll, 40 percent blamed "the influence of popular culture" as the main cause of gun violence, and 35 percent pointed to "the way parents raise their children." Just 18 percent pinned it primarily on the availability of guns.
http://blogs.abcnews.com/thenumbers/2008/06/guns-and-the-co.html