I've seen some ridiculously long barreled lugers at gun shows. There was an Artilery model that was 8 inches I believe. Not that that is too bad. I did see one that had a 12" barrel and also had the stock mounted, so it was like a Luger Carbine. Even had the drum mag on it. PRetty cool, but sure looked funny.
Outside of TC Contenders and 9mm carbine rifles, I haven't seen too many freaky long barrels on any autos...