As usual after any mass shooting tragedy, the anti-gunners have been spouting their propaganda once more, including the tired old canard "Who needs a 100-round magazine?" It makes for a cute sound bite, but has little or nothing to do with reality - particularly because most shooters can change magazines pretty quickly when necessary (as we'll see below), rendering the question moot.
Congressional representative Thomas Massie of Kentucky had a great answer to that question.
Nicely put, sir!
I don't have any very-large-capacity magazines for my rifles, because I've found too many cases where they jam or cause problems. That's not to say there aren't some very good products out there, but many are of questionable reliability. (Also, they're very expensive compared to standard-capacity magazines, and I'm not on a government budget!)
By the way, the often-touted 10-round magazine size limit, that some want to impose on all handguns and rifles, won't do much, if anything, to slow down someone who wants to kill a lot of people. Indiana Sheriff Ken Campbell produced this video a few years ago, using "ordinary shooters" like you and I to demonstrate the point. I highly recommend watching it, and using it to defend standard-capacity magazines against that sort of uninformed attack. After a series of text slides, the live action gets going at about 1m. 45sec.
Ken Campbell has since retired from law enforcement, and is currently the Chief Operating Officer at Gunsite Academy in Arizona, founded by the late, great and sadly missed Jeff Cooper. If you want some of the best firearms training in the country, whether for civilians or for law enforcement, it's a great place to visit.