I got some surplus 303 one time that was really REALLY old. I mean like ww1 vintage stuff. The brass was really brittle, it was almost like cast brass. The slugs were nickel plated. They were loaded with REAL chordite. I don't know if you are familiar with real chordite, but it looks like spaghetti, only smaller, maybe like uncooked angel hair pasta. And this stuff burned really slow. It was like shooting an old flintlock. You could hear the firing pin fall, and then a second delay before the powder(?) exploaded. About one out of two were duds.
I wonder how they get an accurate measure of propellant when the propellant is long sticks? What do they do?...count the sticks by hand and then stuff them into the case?
They did it by weight (same as all sensible people do when reloading! I am not a big fan of powder measures, I weigh every fifth load.) It's called "cordite", BTW, because it was extruded in long cords and cut to length to fit in the case.
Cordite is closer to black powder than modern smokeless powder, you're absolutely right about its behavior . . . acts like BP but it's somewhat safer than the old stuff. However, it remains much more unstable than modern smokeless, so I would keep a close eye on it if you still have some around.
I have put a lot of ammo up the spout of the Long Branch sniper rifle & it seems to be still in quite good shape. I wouldn't rebarrel because it was tuned by Holland and Holland, & I'd hate to spoil it!