Boothroyd's "Directory of British Gunmakers" has only this on Murray:
Murray, David Jnr., 23 1/2 David Street, Brechin, Forfar, c.1900
Perhaps there were several generations of Murrays in Brechin?
Boothroyd does not list any Wyatt.
I suspect both Murray and Wyatt were country gunmakers who ordered guns with their adress from the Birmingham guntrade and merely retailed them. My own .500-450#1 BPE double rifle was sold by A.Robertson & Son, Wick, Scotland, but certainly made and proofed in Birmingham too. It is very similar to the "Wyatt" rifle, see here:
http://forums.nitroexpress.com/showflat.php?Cat=0&Number=150854&an=0&page=3#Post150854
Remember, most German country "gunmakers", even "name" ones, had their guns made by the Suhl and Zella-Mehlis guntrade.