doolsautobahn That means you're WAY too aggressive with the mechanical pencil LOL. Don't press so hard on the leads, and they won't break.. :|
I use .5 leads all the time and they never break @_@
But if you're used to writing with .7 leads and pressing harder on the paper, then I can see why you'd break .5 leads more easily, and I guess it might be harder for you to get used to them and putting less pression on the lead when you're writing :S Just use whatever you're more comfortable with lol