To be honest, I was stunned by the range of the little diecast gun. Not only does it throw rounds better than the 155, it does so forcefully. The secret is apparently the spring, which feels much stronger. The problem, though, is that the 25/18 is the wrong period, being more a World War II piece.The same cannot be said of my BMC 18-pounder. It is the correct period, and with its current spring can still out range the 155. Even the ancient Barclay can.
Probably a couple of things. First of all, the firing mechanism drags on the inside of the barrel. That means lubrication is needed, probably graphite powder. Secondly is the spring itself, from an ink pen. Might need to acquire a stronger spring for more range.
Couple this to the fact that my first cannon has actually resurfaced. Compared to the 155, it is a bit primitive. Still, it might make a nice fortress cannon. Still have two more of those kits.
I suppose I need to think things through a little more on those. Meantime, work has begun on the 8-inch Mk. I. That should be fun.