They were leather guns built by Wemyss in 1650-51. There were 3 of them in Edinburgh castle and they were taken from there, seemingly more to prevent the Jacobites getting them. Each were carried with it's carriage on a horse. Not pulled by it but on top of it so they must have been pretty small. They were technically not 'frames' but personally I think the difference is irrelevant to us as gamers.
They were fired, I would guess at longish range for these guns but that would actually be a short range really, in an attempt to provoke the Jacobites to attack. They were a total failure and all broke after 3 shots.