Thanks, I appreciate all of the feedback - especially from you guys!
Malika, yes these are 100% compatible with Battlegroup Helios and BFG.
Fleafa: would you have preferred a different number of barrels?
RageOfAchilles: I can tell exactly why you like these. They have a very utilitarian vibe going on
The barrels were machined from brass rod on a lathe and once parted off it was very difficult to adjust their length (they were shortened from the original length). Despite RageOfAchilles' suggestion I think I will shorten them by a millimetre (at the base, not the tips as there is machined detail there).
It's a bit late now but it probably would have looked better if the balls were larger. Unfortunately I kind of did things backwards and should have made the module to fit the balls...
Oh yeah I can make that....