The accuracy of the BDC does not depend at all on the caliber. It depends on you and the information you enter into the calculator to find out where the different circles will be "on" with regard to distance.
Find the Nikon "Spot On" program on Nikon's site.
Nikon Spot On™ Ballistic Match Technology Program
Follow the directions -
Step 1, pick the scope
Step 2, pick the caliber, ammo brand and then weight.
Step 3, add the target distance and zero distance (probably 100 or 200 yards).
Note that you can change atmospheric conditions as well as customize your load if you wish.
Now hit Fire! and look at the image of the BDC on the right.
Note that you can change the scope's "magnification" on the upper right and change the yardages for the circles. Having the correct power is key.
I printed out a "picture" of the BDC reticle using the print in the upper right of the reticle photo, and laminated them for Dad's rifles. He now has them for field use and per his antelope hunt this year they're right on.
I hope that helps explain it. The 7mm Wby Mag we use is ballistically very similar to the 270WSM, so your results should be very much the same.