Several states have laws in conflict with this - California, Colorado, NY, etc. So when does this get resolved at the federal level?
This particular case is currently under review by a three judge panel of the 9th Circus. After they rule, whichever way they go, the other party can appeal to an en banc 9th Circuit panel for a second review. After the outcome of that review, whichever way it falls, the other party can appeal to the U.S. Supreme Court.
if SCOTUS takes the case, and if they rule that the magazine capacity limits are unconstitutional, then this ruling will apply nationwide, toppling the magazine limit bans of NY, NJ, etc.