— The new ban would cover more firearm models than the 1994 ban did. Alex Pappas of the Daily Caller screen-grabbed a list of all the specific firearm models that would be prohibited under the new ban — 157 in all:
This list is more detailed than the previous assault-weapons ban, which focused on 18 specific firearms models. Yet one of the big problems with the 1994 law was that it was often relatively easy for gun manufacturers to come up with similar types of guns that weren't on the list of explicitly barred firearms. Could that happen again? That's a key question.
— The new bill broadens the definition of "assault weapon" slightly. In addition to the specific firearm models banned above, the new bill will also prohibit any semiautomatic rifles, handguns or shotguns that can accept a detachable magazine and "have one or more military characteristics" (such as folding stocks or pistol grips for rifles, or threaded barrels). The same goes for rifles or handguns with fixed magazines that can accept more than 10 rounds.
This is a slight change from the 1994 ban, which prohibited any semiautomatics with detachable magazines and two or more "military characteristics." Supporters are hoping that this small tweak will make it marginally more difficult for gun manufacturers to work around the law.
"One criticism of the '94 law was that it was a two-characteristic test that defined [an assault weapon]," said Sen. Dianne Feinstein at a news conference today, according to Mother Jones. "And that was too easy to work around. Manufacturers could simply remove one of the characteristics, and the firearm was legal. The bill we are introducing today will make it much more difficult to work around by moving a one-characteristic test."
— The new ban would tighten regulations on existing assault-weapons and high-capacity magazines. One of the reasons the 1994 ban had such a limited reach was that it grandfathered in roughly 1.5 million assault weapons and 24 million high-capacity magazines that were already in private hands. In fact, gun manufacturers actually boosted production of weapons and magazines in the months before the ban took effect. As a result, there were plenty of assault weapons already in circulation.
The new assault weapons ban would still have an exemption for assault weapons that are already lawfully owned — "No weapon is taken from anyone," Feinstein said. But the bill would require background checks for the sale or transfer of any assault weapons that are grandfathered in. The bill would also forbid the sale or transfer of high-capacity magazines that were owned before the ban.
These restrictions could prove difficult to enforce in practice — after all, there's no national gun registry tracking who owns what weapon. To that end, the bill has a provision requiring all assault weapons and high-capacity magazines produced before the ban takes effect to be engraved with serial numbers and date of manufacture.
— The bill would also require current assault-weapons owners to "safely store their firearms." This is another change from the 1994 law, though it's not clear how this would be enforced.
— States and localities could conduct "voluntary buy-back programs." The bill would allow localities to use federal grants for voluntary buy-back programs for grandfathered assault weapons and high-capacity magazines.
— The new ban wouldn't sunset after 10 years. This is arguably the biggest change. Some gun-control advocates have argued that the 1994 assault-weapons ban might have been more effective if it hadn't been allowed to lapse. In his big study (pdf) of the law, the University of Pennsylvania's Christopher Koper argued that the effects of any ban would be bound to only occur gradually, in part because so many currently-owned weapons and magazines were exempted.
This time around, Feinstein said she's designing the ban to be permanent, rather than letting it expire after a decade. "The purpose of this bill is to dry up the supply of these weapons over time," she said. "Therefore there is no sunset on this bill."
--A full summary (pdf) of the bill.
--Everything you need to know about the 1994 assault-weapons ban
--The assault-weapons ban is only one aspect of Obama's proposals to reduce gun violence. He's also pushed things like universal background checks and giving law enforcement more power to trace guns. See here for the full list.