Paul, chamber sleeving or re-lining is certainly possible, but entails some complications for the home gunsmith.
Alignment is the biggest issue. It the chamber sleeve is not perfectly concentric with the existing bore axis, and concentric with the re-bore, the .45 Colt chamber reamer pilot will not have the bore surface to guide on, resulting in a non-concentric chamber and throat. Disastrous for accuracy and bore leading problems! These same issues apply to most any gunsmith capable of doing re-sleeving work. It's a job for the barrel re-lining specialist.
As for your comment on stellite liners for .50 BMG barrels, that is another matter entirely. Armament factories, especially Government Arsenals, have the advantage of many generations of experience, specialized machinery, personnel, etc of addressing particular aspects of weapons manufacture. Stellite lined machine gun barrels do give greatly extended useful and accuracy life in these applications, and that is why the US Government uses them. The europeans, on the other hand, have never mastered the special problems in fitting stellite liners in their machine of gun barrels, and so, do not use them. Even the great weapons factories of FN Belgium, Spain, Austria, Germany, Italy, and the UK never used stellite liners.
Your proposal is certainly a sound one, but should only be tackled by a highly qualified barrel rebore specialist.
John
