I think I posted on this a few years ago but my list includes several well know ones:

(1) Of course Graeme Wright's "Shooting the British Double Rifle"

(2) Alexander Gray's "The Hammerless Double Rifle,".

(3) Craig Boddington, "Safari Rifles,"

(4) John Taylor, "African Rifles and Cartridges."

(5) Gregor Woods, "Rifles for Africa."

Ross Seyfried in the "Double Gun" Journal. Like vol. 5 issue 4 1994; vol. 6 issue 1 1995; vol. 10 issue 4 winter 1999.

Sherman Bell see 15, issue 1 sprind 2004; and his current serios of express rifle pressure variable in the DGJ.

I also think some of the better double shotgun stuff is useful as far as actions and stocks and things. I wish many of the double rifle writers would get into detail about types of actions, stock measurements and design the way the double shotgun writers doo. Mike McIntosh and Gough Thomas come to mind here.