I'm glad you all are enjoying this!
Top Jaw,
1876 being the centennial did not escape me, and for a while, I wondered if the horn was made to commemorate that year. It was clearly carried, I think, which was made obvious to me by the darker neck wearing lighter on one side. As if the load of powder wasn't evidence enough. I had also considered that the horn might have been repaired at one time, and perhaps that was the second date.
Pukka Bundook,
I am not from Lindisfarne, but I do have a deep interest in all things Norse.
I also suspect the year was a later addition. It is worn quite smooth, now, but if you look, there is a very fine double line running around the body of the horn just before the neck. That delicate line doesn't agree with the rather deep, and I daresay illiterate inciting of the initials and date.
Anyway, I find it elegant in its simplicity, and it brings me a lot of pleasure to handle. Perhaps one day, I will try and copy it for my own shooting kit.
Stay tuned; I have another horn I want to share as soon as I take some decent photographs.