Hi Rob,
Yes, the majority of calibres I am aware of are small, certainly not many above .5, most less. Scotland did not have many large animals apart from deer, and money was always tight!
It is difficult to tell the origin of a firearm apart from its style. The guns from which TRS patterned its reproductions were found in Germany, but supposedly belonged to Scottish mercenaries. The photo of the full stocked musket from the early catalogue certainly looks like a Scots gun as the barrel is stepped and the stock looks to be in the Scots style.. the top comb seems a bit high though, however this may have been a later development.. the use of the flintlock, even though it is of early design, would indicate a later evolution..
The TRS pistol kit is also of a later pattern, and more of the type made in Birmingham. The original fish and heart stocked pistols are truly works of art... The book you should try and find is "The Scottish Pistol" by Martin Kelvin ISBN 1-900541-15--7
This is good too:
https://www.flagstaffscottishclub.c...ottish-firearms-part-i-scottish-steel-pistols