Just a guess because of a similar experience with a B&C medalist on a BDL floorplate type Remington 700 SPS VSF, but I'm guessing that the bottom metal is not sitting up far enough into the B&C stock. This could be keeping the mag from sitting close enough to the action to allow the bolt to pick up the round and the bolt may be simply passing over top of the cartridge. If so you may have to relieve a little material at a time between the stock and bottom metal and test fit until you get it to fit just right.
Pretty sure the manufacturer does this because relieving material to make em fit is easier and cleaner than trying to add material.