Any effort to restrict the sales of certain firearms or magazines will have little impact unless it is accompanied by a buy-back program. After the Fort Arthur Massacre in Australia (which left 35 dead and 23 wounded), that nation banned assault style weapons. A keep component of that ban was a buy-back program, which purchased and destroyed more than 631,000 firearms.
It is estimated that there are 300 million privately owned firearms in the US. Banning future sales of certain firearms will do nothing to reduce the number of those weapons in circulation.