I can`t remember that particular MacNaughton rifle but have seen a couple of others - I`ve never seen ( or heard of ) a bar-in-wood round action rifle.
I`ve little idea of what has been published about William Horton......and have no idea what you might know already.
He was a Stocker in Birmingham before setting up as a gunmaker. Later moved to Whitehaven and then to Glasgow - various addresses. Produced a boxlock action ( I`ve seen two of them I believe ) and was credited with a couple of patents. I`ve had a sidelock of his and have seen others - all built on proprietary Birmingham actions - the one that I had being fitted with Chilton locks. I`ve seen two boxlock rifles, one on a Webley & Scott action, the other on the ubiquitous Alex Henry/Alex Martin type action that was produced by at least two or three Birmingham makers. I`ve also seen an earlier back action hammer sidelock in .450BPE. His own design boxlock seems to have been made for only a few years up to around the mid 1890s - after that all the actions were bought in. The later guns were 100% Birmingham made.
I`m vaguely aware of some relationship with Charles Ingram/George Coster but can`t think what that might be at the moment - I`ll have to brood on that.
I an supply dates for the various addresses but the IGC Historical Database is bound to have them and, no doubt, other information.
Is there a specific question that you have ? My personal historical database is mostly in my head and usually requires specific prompting to retrieve information.....a thump in the ear is often quite effective !