you could rebarrel a BLR to 280..if you start with one in a long action cartridge like 270 or 30-06.....
like Dennis says....a 7-08 cannot be rechambered to 280, unless you have enough shank to move the barrel back about an inch...a 7-08 can however be rechambered to 280 Ackley...if you have the action length.....easiest way to get more speed out of a 7-08 chamber on a short action rifle is a rechamber to 7-08AI or 284 Winchester..but you'd probably run into feeding problems with these in a BLR......but,..BLR's were at one time made in 284 Win and maybe a magazine is available.