Looks as if very little has been done on Davis in Double Gun Journal, except going back to very early issues. Would be worth a good article, I think.
I don't know whether the publication is still available, but Shotgun Sports put out a paperback compilation of some of Don Zutz's columns called "Grand Old Shotguns". That book includes a short article on N.R. Davis, in which Zutz has some positive comments about both the early hammer and hammerless doubles. The hammerless guns, per Zutz, used coil rather than leaf mainsprings.
