Pyrodex blows, literally.
I tried all the tricks, could never get a decent report with a blank load. Pyrodex simply will not burn fast enough without the pressure of a loaded ball ahead of it.
If you can't get black powder in your area, you can buy it online. Thing is, you will have to buy a lot and pay the HazMat fee. But the plus side is that Pyrodex is priced higher per pound (at least here) than real BP and I still come out about equal if not better even after shipping/HazMat.
Www.powderinc.com will sell in lots as small as 5 pounds, but you still pay the same $20 HazMat fee if you buy 5 pounds or 50. But as I said before, the price per pound, even at the highest rate, is still comparable to buying Pyrodex locally.
Shoot safe and have Fun!