Anybody make a direct impingement AK?

Oh, you might check some of the build sites, like weaponeer.net or gunco.net--they have guys over there that do some wacky stuff. Caliber conversions, blow back 9mm and .45 builds and so on. I think someone did a 6.8.

The guy that's building milled CZ-58 receivers would probably know.

IMO the gas piston makes half of the gas system very clean, but eliminates the self-cleaning properties of the other half. Both designs work O.K. Only testing can determine which works better for a given model/cartridge combination. In the case of an AK, I would stick with the orignial.
Richard
Schennberg.com