If 16 rounds is not sufficient, I am dead anyway
Simply not worth it. Mater of odds. How many gun fights last more than 3?
Most don't (that's what the statistics say). So, some have zero, some have 6.
I am only interested in stopping an issue, not pursuing it. If I can stop, hold off or make it go away I am not going to be shooting a lot. Only enough do manage the situation, I don't have to solve it.
Extra mag? Ok, dump the bad one, get the new one and in the meantime? You are shot full of holes.
Back to statistics, I am more likely to get killed in a car crash than need an extra magazine. Carry a spare car, drive a tank, where does it end (with a small class 8 Pickup?)
Do the best with what you can and what gets you is probably not what you spent all the time thinking about.
Too many people focus in on the security issue and ignore the rest. Get an auto with a 5 star crash rating is money well spent.
Fool yourself into thinking you can manage a gun fight involving 3 magazine changes. Hmm, and then there are those who spent a life on the tactical drills only to freeze up when the real thing occurred. If I wanted to really find out how I would do I would have gone into LEO (actually did some training in it and decided it was not for me). I did find out I had a lot to learn.
That you find out in your fist gun fight. Somewhere in there is having a life. You should balance it out.