Mr. Hughes:
See "Field Artillery Weapons of the Civil War" by Hazlett, Olmstead and Parks. Universiy of Delaware Press, Newark De?? Second edition 1988. P. 172. ISBN #0-87413-346-7 A small paragraph Concerning D. W. Hughes and his 1.5" and 2" Hughes guns. I hope it may provide some info but may be too general. As mentioned, none of these guns appears to have survived. If you know of any, please let me know.
Ron