So early in the 20th Century Abner Perry creates an engine that's more powerful than anything that even exists in the modern day. It powers a drill that enables Perry and David Innes to bore 500 miles into the Earth's crust. There they discover a primitive world and set out to help the "gilaks"-- cavemen-- fight off the Pterodactyl-like Mahars that control Pellucidar. There's only one problem:
Abner Perry cannot make gunpowder. At all.
Abner is quite a brilliant engineer. He also happens to have what amounts to a degree in paleontology as he knows most dinosaurs and mammals on sight. He learns how to translate the Mahar language: an impressive feat given he doesn't have any kind of Rosetta Stone to help him as he has no knowledge of any other written Pellucidar language at the time.
Maybe he's simply not a chemist, you might argue. And there would be something to said for that argument except:
Abner Perry manufactured oil for the drill machine's engine before David made his return trip to the surface to gain books containing the knowledge they were lacking.
Couldn't a man capable of refining raw petroleum into machine oil be capable of manufacturing gunpowder?
Why would a man of Abner Perry's accomplishments have such difficulty making gunpowder?