I see the major design flaw being the way-oversized gas piston. The purpose of this piston is to delay the opening of the slide so that the primer will no blow out of the case (has nothing to do with case rupture). If this piston design were used with an ordinary barrel (and chamber), the slide would never open. So as a band-aid, H&K added grooves in the chamber to help fight the large piston. Unfortunately, these grooves bleed out about 8% more kinetic energy than other guns with similar barrel lengths. Some people say about these grooves help the case eject if the extractor breaks - that might be true, but I don't think that is what H&K engineers had in mind. Despite what some people say about gas delay guns losing 5% energy due to the gas bleed hole, it loses less than one-half a percent of the kinetic energy through through this hole because of the tight clearance between the gas piston and the gas cylinder.