sherppa, I had a BLR rebarreled from 308 to 260 a few years ago. Sent it to a gunsmith in montana. His only concern was if it was the steel reciever. Mine was.
If he could rebarrel a BLR no doubt he could rebarell a BAR. However it cost over $400 to have it rebarelled and a rebore from a 243 would be cheaper as Bigfoot stated.
Regards, Byron