While they bash the brass up with a good sized dent, they WILL resize and be perfectly reloadable. As long as the round will drop ALL the way in the chamber, it'll fire. The case will merely fire-form itself to the chamber dimensions a fraction of a second before the gun drops another dent in it as it sends it on it's merry way.
I've had no issues with cases fired from HKs. Just be careful of case mouth dents. A dummy cartridge is the perfect tool for removing about 75% of the dent before letting your press finish the job. Do not try to get the case mouth dent all the way out with the dummy shell. You don't want to work the brass any more than you have to.