First some housekeeping. Per our rules we Do Not Discuss the Making or using of DIY Black Powder. PERIOD. Just a warning for a new member but it will get your account deleted if repeated.
I am fairly new to flintlocks, about 6 years vs 44 years with caplocks. But I know if I don't prick my charge with my vent pick after loading there's a good chance it won't go bang. The load needs a place for the flash charge to land in the chamber, I would imagine especially with home made powder.
My advice is to make a vent pick; mine is a piece of baling wire I heated and hammered the end in a vice.
Get some factory made real black powder, substitutes won't work for this. You can try picking a few grains of what you're using for main charge out of the chamber thru the vent, then try to force a few grains of the real stuff back in. You don't need much holy black to ignite the remainder.
Mark your ramrod with a marker where bottom is, then where your loaded round is, this way you know when you're fully seated.
Does your rifle have a vent liner? If you can unscrew the liner you're golden. Unscrew it, scrape out the offending powder, replace with store made. Again, lyou only need a small amount as a primary charge to ignite the rest.
Did you moisten or lube the patch before loading it? Did you swab the bore of the rifle after you got it? There could be a glob of packing grease that is causing problems?
if you swabbed the barrel I'd try getting a few grains of store bought fffg in your barrel before pulling the ball.
I'm sure others will have more advice, but first we need answers to our questions to help diagnose your situation.