http://sellers.kippenjungle.nl/page3.html
two copies of the gene give heavy leg feathering. One copy gives light leg feathering. No copies give none. So 1/4 of your chicks should be feather legged if the roo has one copy, half if he has two copies and the hen has none.
Conversely, if he has one copy, some of those chicks could hatch clean legged and still be his.
Anything else in a BCM that would be a distinguishing factor? Color of feet? Any sign of black on the shanks or feet should show BCM. Possibly beak color as well.