[Chrontius]

Black powder is used in booster charges. In artillery fuzes, there can be up to four different types of explosive in the explosive train which ignites the main charge, according to my half-assed Googling and Wikipedia.

https://en.wikipedia.org/wiki/Explosive_train

In addition, black powder in particular is used in recoilless rifles, perhaps the most famous example being the RPG-7.

http://previewcf.turbosquid.com/Preview/2016/01/31__04_23_48...

In this image, the olive-drab component is the warhead-and-rocket assembly, and the forest-green component is a full fucking pound of black powder which launches the rocket to a minimum safe range before the ignition of the main propulsion motor.

I'm presently unsure about the propellants used in other recoilless systems, but I can presume that there exist designs other than the RPG-7 which are currently being provided in bulk to Ukraine, while simultaneously utilizing some amount of black powder in the propulsion system, while some further subset of those will prove difficult to redesign to use more modern double- or triple-base smokeless propellants due to the much higher operating pressure of these propellants, especially in the context of thin-walled light-weight launchers.

[fwlr]

Yes, I suspected that if there were dependencies on black-powder, it was because it was being used in older weapons systems and those were being supplied to Ukraine.

There are plenty of black-powder substitutes that are carefully designed to match various characteristics of standard black-powder, including 1:1 volumetric substitution and similar pressures https://en.m.wikipedia.org/wiki/Black_powder_substitute

If black-powder is strictly necessary and not just convenient, these substitutes would be used.