First, I agree with JDD above, Biden/Harris would need the ability to pack the Supreme Court and that only happens if the President has his own party majorities in the House and Senate. The number of Justices is determined by the current provision of the Judiciary Act, which set the number at 9 a few years after the Civil War. So an amendment to the law would have to be written, passed by both Chambers, and send to the President to sign into law. So, we'll know in a few days whether that is even possible.
Second, in re high capacity magazines, there is a kind of insanity involve