Rene, good observation re: the dolphins. I have not yet run across a document addressing that change, but there will almost certainly be one filed away somewhere in the National Archives and I'll keep an eye out for that information in future visits. If anyone else is aware of the directive for that change, please share it.
Olmstead et al, "FIELD ARTILLERY WEAPONS OF THE CIVIL WAR" pp. 92 has a good discussion of the handles, as you've probably seen. The omission of the handles is discussed in terms of the earliest registry number for each of the few contractors, on which the handles are absent.
This statement is interesting (also pp. 92:) "While the earliest Greenwood [one of the contractors] recovery is registry number 3, the original contract with the firm included the statement 'according to the drawing herewith enclosed, omitting the handles.'"
If I had to guess what prompted the omission of the handles, I'd guess it was a request by one or more of the contractors to do away with them since casting a cannon with handles required more time setting up the flask for casting, and more chances for manufacturing defects due to the increased complexity of the setup. The Federal government wanted Napoleons delivered as rapidly as possible, so I suspect they readily agreed to eliminate the handles. But this is of course pure speculation, so we'll keep the question open until someone runs across better documentation.
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