As stated, Denver's AWB only applies to mags of 21 rounds or more. This doesn't directly affect you as you are not a resident. The law states that it is an Affirmative Defense if you are transporting them through Denver city limits and are not a Denver resident. The general consensus is if you get stopped with mags in your vehicle, is to keep your mouth shut.

While I have not heard an anecdote of someone getting stopped by DPD with mags in their car, it is possible they could confiscate them and charge you.

You can read the thread on this topic here and make your own conclusions.