OK, the problem, as I so poorly tried to explain it, before, is gunpowder needs spark and oxygen, to burn, three sides of the "fire triangle", fuel, O, and heat.
In the vacuum of space, you don't have oxygen, neatly compressed into atmosphere at 14.7 PPSI, like down here, on earth. Even if there is oxygen in the powder, how do we know it will react to less than 0 PPSI, as in a vacuum, like space?
The same way gravity affects recoil, might not vacuum affect firearms combustion paradigm ? There's even the possibility that in that decompressed atmosphere, the explosive properties of gunpowders may be multiplied, since there is no atmosphere
compressing the air, and holding everything within the `14.7 PPSI envelope. We know how brass, steel, and gunpowder react here, on earth, but we are taking for granted the density of our atmospheric cushion, which doesn't exist, in space.