"thought experiment"
^^^ That's really an unreasonable expectation for some people to engage in. I understand it's just an experient. I don't think some can wrap their brain around that though.
I personally could live with the trade mentioned, as I have little personal use for hi-cap magazines (same with "machine" guns). I would hope the capacity if such a thing was ever passed was at least limited to 12 or 15, if not 20. Even a subcompact XD holds 13 rounds in a flush fit magazine in 9mm, for cryin' our loud.
And yea, I oppose a hi-cap mag ban in principle. But you're talking about quid pro quo bartering. So I'll play along with the exercise.