Depends on whether the tube breaches before the powder lights; without full containment, smokeless is just going to throw lots of sparks and smoke, which somebody cutting steel with an angle grinder is already ready for. A good bit more than the grinder would produce, but not really that much of a deterrent. A big enough pile of BP will make a mess even laying out in the open.

(Could've sworn I had some 4350 open to demo that with, but the only jug I'm finding is still sealed. May try it sometime with the "random stuff from pulled milsurp" ammo powder can though, since that's not much good for anything else.)