These are US Navy bombs developed just after the end of ww1. On a 1923 official ordnance department photo (found in the Rick Stauber archive at uxoinfo.com) the 230 lb is defined as "230lb tipped with nose bucket". However in US Navy documents of the period the various bombs developed are defines as follows:
Navy Mk IV 163 lb
Navy 230lb Light case MkI
Navy 250lb Heavy case MkI (copy of the english 250lb bomb) with fuse both at nose and tail, allowing for a delay of 1.2 seconds..
Navy 520lb Light case MkI fused in the nose only giving 1.2 seconds delay on impact with water or withd ecks or other solid surfaces. (340lbs TNT) strictly anti-submarine and has not enetrating quality - it depends for effect on blast only.
Navy 550lb Heavy case Mk I
(The Navy 250 Heavy case MkI, 520lb Light case MkI and 550lb Heavy case MkI are of British design)
By September, 1917 two types of US Navy bombs were in service with a third type coming into production, weighing 163, 270, and 216 pounds respectively.
By the end of WW1, three sizes became standard in the U.S. Navy: a 163-pound light case bomb, a 230 and a 270-pound bomb. The most common ordnance load for large patrol flying boats was two 230-pound bombs, one under each wing. U.S units assigned abroad used English, French and Italian ordnance. Units assigned to British bases used 100, 230 and 520-pound bombs and units assigned to French bases used 52, 75 and 150-kilogram bombs.
But the story is more complicated by that as USN flying boats in the 20s used a specially designed series of Navy bombs, for which I have found only photos but no other data (except on their fuze) - see the thred about them on this forum