Sleeving has become cost-prohibitive, as well as being no longer practical for field-quality guns. A really fine-quality gun (Purdey, Boss, Woodward, et al) are so reduced in value by sleeving that it no longer makes sense unless they are acquired very cheaply or are a family heirloom that needs rescuing for dedicated shooting. When it was reasonable from a cost standpoint it was a great way to put a $3000 gun back in service. No more.
JR

Be strong, be of good courage.
God bless America, long live the Republic.