SniperJohn you have a good nose, your right the propellant charge in a panzerfaust is indeed black powder, this was probably due to being easy to produce compared to proper rocketry propellants, and at the end of the War I'm sure as long as the war head left the tube it did not matter much what lunched it.
As to deactivating one of these then as I've said many time before "High explosives can really spoil your day" also I think a lot of people forget that most high explosive have both a solid and liquid component, and as such can become very unstable with age, especially when they have been in the ground for 50+ years, and thus get a little sweaty just like dynamite, so could explode on contact, or if dropped, or for that matter if struck with a metal object such as a shovel. Plus if it was safer to disarm such items the EOD/ RAF/ Bomb disposal etc would deactivte such items on site when found instead of blowing them up!
Finally I remember a case back in the 1970ís were some young lads discovered a belt of Machine gun ammo (.50 BMG?) at one of the old wartime airbases in the U.K. one of them thought he take a hammer to the bullets to set one off, and that was the last stupid thing he ever did, as striking one set of the whole belt and that was the end of him.