Wonderful picture (it's so uncommon to see pictures of ww2 wartime Navy bombs) but this is a 500lb Mk12 Navy bomb not a AN-M series bomb - the reinforcing pieces between the fins are straight, with have parallel sides.
They are different from the ones on the M and AN-M series:
Navy bombs:
500lb Mk12

1000lb Mk13 (On these bombs, an additional set of tubular reinforcing struts at the rear of the fins is added to the regular box-type reinforcing struts):

500lb AN-M43/ AN-M64

1000lb AN-M44/ AN-M65
The photograph is also evidences that the tail seems to have been left in the original yellow paint.
The grey paint of the Navy bombs was initially a measure taken aboard the carriers, over-painting locally the yellow painted (yellow = HE) bombs with grey paint available on board (same as underside paint of navy aircraft) but already by 1943 it appears in USN official regulations, and will remain so till end of WW2. However, Olive drab painted bombs were commonly found among Marines squadrons that fought on land, and could also be seen for AN-M series bombs aboard carriers (when not painted over locally).
Grey painted navy bombs

As it can be seen here this practice was not reserved to Navy Mk12 and Mk13 but also to depth charges and air-dropped mines:
AN AN-M64 and An AN-M65 (photographs from museum samples)
Wartime AN-M photos (on the second photo on can see the double attachment points: 2 lugs on one side, 1 lug on the other side)
