Some very good information posted here, but there are three different things being discussed as one! In these posts we have had examples posted for sleeving shotgun barrels, Mnon-blocking of old rifle barrels, and sleeving in new barrels (this could also include converting a shotgun to a rifle, as well), and true mono-block barrels! All do not require the same methods of fitting, and all are physically different in make up!

In the case of a real mono-block, as the name implies, a mono-block is one solid piece of steel, milled from a known aloy. With this one may fit the block to the action and rough finish to shape befor barrels are even aquired. There is no solder involved at this point. the barrels may be turned to fit two holes through the mono-block, and can be fixed there by threading, and press fit, or silvering,the barrel shanks, and fluxing, the mono-block, heated, and barrels pressed into place, and cooled. At this point the stress relief can be done any way the maker chooses. I personally whould go the Cryno method with any of the systems involved posted on this thread. The true mono-block can be tigged, with little problem in relieving stress by the method you choose.

The sleeving of new barrels in an old shotgun,be they rifle or shot, is best done by cutting threads in the front 1" of the hole with the rest of the barrel shank being turned to a press fit in the squared, and faced old barrel butts! No heat involved at all. That method is not only stronger, but when the ribs are installed,it locks the barrels in place perminently. This last thing is not true mono-blocking, and though both the mono-block, and sleeving in new barresl in the old barrel butts are both sleeving, the are as different as night and day as far as strength goes, and methods need to be done properly!