It will happen in 1968.
Again in 1986, 1989 and 1994.
I don't think all firearms will be banned anytime in the next 100 years.
Military style high capacity ones (922r guns) will be banned in 2004. After that the only military style ones will be single stack 10 rounders that won't take a high cap. Eventually you will have Kali style laws on all new guns (ie. no pistol grip, etc. on detachable mag guns.)
I predict in 10 years no firearm capable of holding more than 10 rounds will be available to civilians.
Prebans, pre86, pre89, pre94 and pre04 will bring huge premiums in the states that permit their ownership.