Hi Michael,
I am indeed suprised in a good way to find you in this topic
When the blunderbuss will arrive at my home, i will investigate the name Ketland on it. It might be William or Thomas Ketland instead of Ketland & co (it would make more sense if the butstock is of 1770's design).
I wondered, the pancover has a roller... i always believed they only came into fashion from around 1800's ?
Fernando, do you have a picture of this other specimen? I couldn't find it