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.
Instability has to do with the powder breaking down into its component chemicals (e.g. cheap aspirin breaks down leaving acetic acid, hence the vinegar smell in a big bottle of cheap aspirin). It MAY be harmless, but IF it breaks down into an acid or a less stable oxidizer (e.g. chlorate) or heaven forbid both, it may spontaneously combust or heat up. At any rate, once it has decomposed it will not fire off properly. I do not know the decomposition products of cordite, having never dealt with it, but both my husband and I used to be fireworkers, and decomposition is an ongoing and dangerous problem in fireworks.
As for cordite, I find in Chapter 15 of Sharpe's "Complete Guide to Handloading" that the British patent stuff is 30% nitroglycerine, 65% guncotton, and 5% petroleum jelly, with acetone as a solvent. I have no idea how unstable it is, (although guncotton is notorious unstable) but it is certainly sensitive, that is, it is subject to ignition through static electricity, impact, or being struck with a metallic object. (Modern smokeless powder is mostly made of nitrocellulose). If you have any more of that stuff around, THROW IT AWAY!