I wouldn't shoot that 303. Ammo that old might blow up your gun, and your face. The powder can deteriorate and detonate. There is a story around here of an old box that took out two rifles, and nearly killed a nearby kid in the process of blowing up the first rifle.
Find the whole story here:
https://www.canadiangunnutz.com/for...rue-story-of-the-possible-dangers-of-old-ammo
Personally, i won't shoot anything that's made before the end of ww2 because who knows, and my face is more important than firing some old ammo.
I'd be happy to loan you my #4, and I can bring it with me to work in Vernon.
Thank you for your generous offer ^^ But Suther has a good point. What I will do is; buy an old sportered L-E and remotely trigger it when I do the testing.