Tim-
First things first, Congratulations on finding such a nice .303
Next, I'm going to send you over to NitroExpress.com for your loading questions.
I haven't owned a .303 double rifle, although I have owned and run an 8x60R double rifle (nitro, boxlock ejector...) and my first notes to you are going to be to photograph and publish the full course of proof marks and engraving on that rifle -- everywhere you find it.
It's likely that period Kynoch ammunition would regulate in the rifle, but I'd want to see the proofs and other marks first.
Also, you need to cast the chambers and slug the bores.
It's very, very important to know for double damn sure EXACTLY what you have there from breechface to muzzle.
Publish that information as well.
Till then, enjoy the rifle in your hands!!
--Tinker
