Not my area of expertise, but while you can use soft lead solder, epoxy, or green Locktite to fix the sleeve in a .22 rimfire barrel (there's a great video online), an old gunsmithing book I have said that the pressure created by a center fire cartridge requires the use of silver solder to fix the sleeve. Granted, things have probably change since the book was penned some 70 odd years ago. It might be easier and safer just to rebarrel to .303. Sorry, I never asked - are you sleeving a .577/450 Martini-Henry barrel, or a .303 Britishicon barrel?