There's a couple with very similar shaped barrels to this that use the twin trail. There's quite few that are single trail, but usually have it split where the barrel rests on a section that opens up like a hinge ith the lower portion dropping down to adjust the height/trajectory of the barrel as opposed to the more modern look of this one. I haven't been able to see any rhyme or reason as to when they used the twin trail vs the single. It seems all different bores and lengths were done on both although the twin certainly seems to show up more often in illuminations. This one's uniqueness was kind of what made it stand out to me.
This one has some oddities if you look close. I don't see anywhere that it hinges like most single trails, but there are metal bands that look to band together an upper portion and a lower portion separately. Yet, just behind them are bands going around the whole assembly that would prevent any movement. Nor is there anywherte for the heighth gauge/pin to have been placed except the hole in the terminal end of the trail.
Of course, this whole carraige could be a remake from several hundred years later, or even more recent, and not resemble the original whatsoever.
Edited to add: Hah, it turns out my copy of "Guns" is missing one of the last pages. Of course, that page is all the photo credits. I got a scanned copy of the credits. The cannon is from the Bernisches Historisches Museum. Looks like they have quite a nice collection of early artillery. I'll definitely be getting some documents from them!
