I read on HP Muzzleloading that there is quite a varience in the flash hole diameter (from .027 to .035) from different manufacturers.which can make a differance as to how well you can light-off BH 209.
Makes sence to me.
Measured my Remington Genesis and it's .027. Using a Federal 209 I haven't experienced any hangfires yet, but if I do I'm probably going to get an extra breech plug and drill the flash hole bigger.