A good unconventional blowback was the EVIL OMEN.
The feed system seemed a clever way to reduce chopping, and blowby, but unfortunetly was never used on another gun. The system was given a patent though. Maybe thats preventing anyone from using it? or maybe it didn't really work?
__________________ www.montneel.com "the evidence strongly suggests that neither Billy nor Adam (Smart Parts) could have invented the electronic paintgun" -Garr M. King, U.S. Judge