Those who say never load directly from a flask of that type have a point. If there's a live ember in the bore it could ignite the charge and the flask could blow up. No one would want to experience that. And I generally load from a stand alone powder measure. Yet, in 50+ years of muzzleloader shooting I have never had a charge ignite as I poured it down the bore. Nor has that happened to anyone I know.

Could it happen? Yeah, I guess so. And I've seen claims that it happened with some frequency on the battlefield and on occasion at reenactment events. But those circumstances are a far cry from the norm. Would I use a flask measure to drop the first load of the day into a gun that hasn't been fired? Sure, why not. Would I use a flask measure when I'm wiping the bore between shots with a moistened patch. Sure, why not. Would I sue a flask measure to load shortly after shooting the gun without wiping the bore. NOPE! Chance of ignition is small. But it's there. Why risk it.