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!
Unless your handloading with the stuff, I don't see what difference it makes how "stable" the propellant is. That word doesn't have a very precise meaning. I hear people throw it around alot, but what exactly are they talking about? Shelf life? Tendency for unintended or accidental ignition? I wonder if people even know themselves what they mean when they say "stable".
Store bought ammo is loaded and sealed up for you. You are never in contact with the propellant. Who cares how flammable it is? It's sealed. THe dangerous part of it(handling naked propellant) was already done for you.
By the way, I know first had the dangers of black powder. A spark set off an ounce or so of it( 500+ grains) just this fourth of july and I was only about 2.5 feet away from it. I got some powder burns and a bruised ego to show for my carelessness, but otherwise unharmed.
Also, Chordite is not even close to black powder on the "danger" meter. Not in my opinion, at least. Naked(unconfined) chordite burns slow..sorta like a forth of july sparkler. It spits and sputters and burns along the length of it almost like a slow burning fuse. Naked black powder goes up all at once like a bomb.
I don't see how you can get an accurate measure of chordite when the smallest incremental amount is approximatly one twentieth of the total charge. If you're off by a grain theres nothing you can do to get closer to the desired amount. Except maybe break a stick in half and weigh it to see how close you can get. That doesn't sound practical in a factory that is pumped up for maximum wartime production.