I have a gentleman here in PA that reamed out an old T/C 50 cal Hawken barrel and put in a 50 cal sleeve and rifled it to 1:28. I haven't got a chance to shoot it yet cause everywhere is iced up and deep snow so I can't get to my shooting area.
Anyway, you can't even tell there is a sleeve there as I assume he welded it in place (or silver solder) and reground the muzzle and put a slight crown on it. All I did was cold blue the muzzle and it looks as good as new.
When I asked how much and if he wanted the money up front he told me $150 and he would bill me when he sent the barrel back (trusting soul). Well he had the barrel for about a month and shipped it to me at a cost of $100 + $10 shipping.
Send me a pm and I will give you his name and address and phone number.