Your problem might be that you have more than one assailant. Home invaders are rarely working solo these days. The more ammo you can carry without having to pickup additional gear, the better. You never know how many of "them" are there.
Remember the old-ish tactical adage: "If you aren't shooting, you're reloading." Even supposing you nail an assailant with the first shot, you aren't going to know if he's alone. Given the opportunity, you want to top off your magazine; and it sure would be handy to have some more ammo right there on your boomstick.