I have to agree with Ron. All mono-block systems regardless of the method of joining the barrels to the block have the same weakness, however this is not a problem if designed properly, such as machining a radius at the apex, providing of course that there is enough material thickness. As far as the sleeve, this is the basic principle of laminating and the more steel you use, providing the two parts have good contact, will always increase the overall strength. It won't be as strong as one piece of solid steel but it will still be stronger. Remingtons "Three rings of steel" works in the same way. One ring of steel inside another inside another. We laminate Jeep differential housings here at work by fitting 8mm wall thickness hollow bar inside the legs and attaching with multiple small puddle welds. We have tested the force required to bend the leg before and after laminating, and there is about a 30% increase in resistance to bending.