That was his past position, some time ago.
Trump’s eldest sons are gun owners and are pro-Second Amnedment. They have their father’s ear, and I believe they have changed his mind. Such a ban would not get through Congress. The NRA still wields influence.
Trump once said he does not consider an AR-15 to be an ‘assault weapon.’
George W. was for such a ban, but he did not get his way.
Okay, I checked and found the following, so you are correct, at least as of mid September.
Donald Trump has come out with guns blazing against assault weapon and extended magazine bans, casting them as a "total failure."
The position on assault weapons represents a departure for Trump from a stance he held about 15 years ago. Today's release was not expected from the campaign. Trump has been saying on the trail his next policy paper would focus on taxes and would come out in the next two-three weeks.
"Gun and magazine bans are a total failure. That’s been proven every time it's been tried," the policy paper said. "Opponents of gun rights try to come up with scary sounding phrases like "assault weapons", "military-style weapons" and "high capacity magazines" to confuse people.
"What they're really talking about are popular semi-automatic rifles and standard magazines that are owned by tens of millions of Americans."
The presidential frontrunner instead said: "Law-abiding people should be allowed to own the firearm of their choice. The government has no business dictating what types of firearms good, honest people are allowed to own."
Trump Reverses Stance on Assault Weapons in New Policy Paper