Quote from miggles
The recipe isn't even depicted. I assume you put the gravel/netherrack/obsidian in the bottom left, the gun on the bottom right, and the gunpowder above? If so, then no it does not work.
The recipe is in recipes.txt inside the mod archive. And I've even added a picture in the first post especially for you.
And yes, it does work. If not -- well, you're likely having a conflicting mods problem.