Have been thinking about the length requirements lately and figured someone in the world must have tried a two piece barrel. Have been unable to find any info. This is what I am thinking - take the BLR I mentioned earlier in a takedown with folding stock. Now get your hands on a barrel blank for that rifle, cut it at 9 or 10 inches, thread it female/male to be able to join it up again with a tight fit or use a system similar system to high end takedown rifles where you mate the two pieces and twist lock them together. After all that, drill and rifle the barrel and prepare the chamber for your desired caliber. You could then profile the barrel to what you wish, cut the outside piece to keep the gov happy with a 18.5 barrel length and install a front sight if scope is not an option. A bit far fetched, but I think not impossible. Total piece length would be 12 or less. Four pieces or three if stock is folding and not detachable.
And then someone will blow the theory out of the water by stating that the barrel must consist of at least one piece longer then 18 inches.
Or just say it can be done and explain how. Any gunsmiths out there with barrel experience. Maybe someone could try it, the barrel part anyway...
Now, must find a way to join the barrel pieces... Off to google I go.