Did the assault weapons ban back in the day real change much in terms of gun violence? Is limiting everyone to 5 or 10 rounds a mag on AR-15s really going to change anything when there are millions if not billions of high-cap mags already floating around in the market today? Hell, even if there weren't, some psycho can just climb a bell tower and take potshots at passersby and easily take out as many people as the Boulder shooter before the cops can stop him.
Like it or not, America has the strongest gun culture in the world and the genie has long since left the bottle to try to change that. There are too many guns in circulation and limiting the rights that law-abiding Americans enjoy isn't going to change much if anything.
Honestly, I'd hate to see America lose the ability to own high-powered rifles, not a lot of places allow that sort of thing anymore. You don't know the envy I feel being limited to only shotguns and pistols where I have to pass a piss test and a background check everytime to buy one and wait a whole month for some arbitrary reason. Ah well, at least I can enjoy that much, it's why I can never live in Japan cause you can't own guns there.