In the Nosler reloading guide they only list a 250 gr. Partition Spitzer bullet they don't list an Accubond at they weight. They do list a 225 gr. 200 gr. 180 gr. AccuBond for 338. Perhaps that's why you can not find the numbers for the 250 gr.
The 250gr Accubond was announced after the latest manual was put out, I have 2 paks, currently, and the BC is .575, only just behind the 200gr .30 cal Accubond @ .588.
Both great long range hunting bullets.
They haven't updated their website either, but if you e-mail them they will give you the specs, as I did.