I made another pilgrimage to Machine-gun Bill's (some here may remember my BIL from Westfield, CMP matches, or other shoots) my sister asked what this was and I couldn't answer. We suspect it is shooting/gunsmithing related.
While he had a couple dozen machine-guns in his collection (Many of which are now in the display @ Shooters outpost museum) I don't think any of them were water cooled.