I was flying a Cheiftain on a night freight run from MB to WYY. The freezing level was around 4500 so I'd planned 4000. I departed, there was no moon but a few stars & plenty of city light so I could see there was no cloud. I decided stuff it, I'll go at 6000. I got about halfway down, 'bang' sounded like I'd hit a concrete wall. If I didn't have the harness on I'd have gone through the roof, scared me that much. The windscreen was covered in ice, the leading edge was thick with it & the props were throwing ice off. I descended to 4000ft, at that level it still took some time for the ice to melt. I was crapping myself thinking that the ice wouldn't melt off the windscreen in time to see outside for the approach. Never did that again.