Here is the normal 155gr MK , the BC never gets over .450
http://www.sierrabullets.com/index.c...5&bullettype=0
Here is the 155gr palma MK the BC tops out at .504
http://www.sierrabullets.com/index.c...6&bullettype=0
Clearly there is a design difference in these bullets . I have to assume the palma bullet is longer and that is what gives it the better BC
In the picture of the two bullets next to each other the palma looks a tad longer . You may have to scroll down to the 155gr bullets
http://www.sierrabullets.com/index.c...1&displayAll=1
EDIT : Does anybody know where to find the specs for the OAL of each of these bullets