I have a Charles Moore hammer gun with invisibly sleeved barrels. The sleeving work is so well done that no one I've handed the gun to has ever noticed it was sleeved, even in full daylight. Only when I point out the very, very slight bluing difference between the breech end (the original barrels were damascus) and the barrel sections inserted into the stub do they see it. I don't know who did it, but it's a level of craftsmanship I find astonishing.