Did you try shaking your horn to loosen up the clumped powder? It sounds like the powder has clumped. Even FFg should flow through a quarter-inch hole. The powder got inside that horn, somehow.
I think Pedersoli has pretty well cornered the market on traditional powder flasks, but based on the four I have in my possession, their quality is good. All of mine are traditionally styled, one each of the Colt and Remington pistol flasks, one copy of the US issue "Peace" flask, and one of the French-styled "fluted" flasks. I think that last one is my favorite. A lot of people like the cylindrical flasks, but I don't have one.
If you get a flask, I would recommend that you get some extra spouts for it in different sizes and a flask filling funnel with a threaded shank to screw into the spout hole. Also get an adjustable powder measure and use it to verify the actual charge each of your flask spouts will throw.
When using a flask, shake it a little to ensure the powder will flow, then put the tip of your index finger over the end of the spout. Invert the flask, with your finger in place, and press the thumb lever to open the powder gate. Give it a little shake to make sure the spout has filled, then release the thumb lever. You then release your index finger from the spout to let the premeasured charge flow out.
Don't load a recently fired gun directly from the flask. For safety's sake, release that measured charge of powder into a separate charger, and pour from that into your gun.
I have FFg powder in my two larger flasks, and it works fine. I believe powder clumps when it has been sitting for a long time, but especially if it absorbs moisture. You'll want to make sure your powder canister is stored in an airtight container (a heavy-duty zip lock bag will suffice), preferably with a desiccant. You can usually break up the lumps enough to pour by shaking the container. Your problem sounds like clumped-up powder. Fresh powder will likely flow better, regardless of its granulation.
Are you using real black powder or one of the substitutes? The real thing is better in every way. In my limited experience with substitutes (e.g. Pyrodex), they tend to clump worse than black powder, in addition to their other problems.
I am not recommending that you do this at home, but the old-time military installations that kept black powder in bulk would periodically detail some men to take it out and spread it in the sun to dry it.
Best regards,
Notchy Bob
