If the weapon was designed around 12-17 rounds, that's "standard capacity", not "high capacity".
Against a single opponent, 12-17 rounds should be enough for someone with basic firearms competency and no experience to put you down. However, this is statistically speaking.
- I've seen videos where a cop and a criminal are literally about 6 feet away from each other, dump their magazines at each other, and then get back in their cars and continue a high speed chase.
- I've read stories about a mother who emptied a 6-shooter in (I believe it was .38 special) at a home invader, hit him 5 times - all in the face - and he ran away.
So while statistically 12 rounds should be more than enough to stop a single person, it's not outside the realm of probability for the shooter to get 0 hits in.