The theory behind magazine limits in gun banning terms is that if you make a shooter reload more often, they will be able to fire fewer shots, and there will be a “window of opportunity” where people near the shooter will have a chance to rush and overpower him.
How does that play out in tests administered by law enforcement officers with both experienced and novice shooters?
I don’t practice magazine changes (yeah, bad Bob), but I can change an AR-15 magazine and resume firing on a small target (say, 100 yards away) and be making hits in about 3 seconds. It’s a only a skip of the beat of my cadence as a rifleman. When pistol magazine changes, I tend to be faster, and I suspect I’m back on the trigger in two seconds or so on a pistol with a double-column magazine, retrieving the second magazine from a pouch on my offhand hip.
I’d like to reiterate; I am in no way “fast” to reload a magazine. I am average, at best.
Like other gun ban ideas, the magazine restrictions are created by people who know nothing about firearms. They won’t stop mass shootings, but they might get a good person who only has one magazine on them killed.