There are so many factors to barrel life that the end result is always going vary substantially. I think how hard your pushing a cartridge plays one of the biggest roles. If you plan on running a mild load under 2800 fps with the 250s and use a single base powder like h-1000. I would think your barrel would last 5-6000rds with ease. My 250gr load for my 338 EDGE IMP is about 20grs more powder per shot than a 33nos and it's a mild load. I mostly run a very mild load of h-1000 and 300 gr Bergers at 2830fps. With this combo my barrel has 2400rds on it and still shoots 3in 3 shot groups at 1060yds.