Given the huge number of powder flasks produced during the 18th and 19th centuries and designed to dispense powder directly into the firearm, if the possibility of flash back was a significant concern it is curious that none were offered with some sort of transfer vessel. Something to hold the powder from the flask and then poured down the barrel. Cased sets of pistols, rifles and shotguns often include a flask, but not an intermediate container. I have wondered why this might be...The same concern about using a flask for loading a rifle also applies for loading a pistol such as the Lyman Plains pistol. Transfer the load measured by your flask in those spouts to another measure to pour down the barrel. True, it is very unlikely that an ember will remain in the barrel, but it can happen. The valve on a flask won't seal the powder contained is there is a flash when powder is poured.
Thanks for this information. Very interesting. I have never seen such a devise. Might you have a link?In my opinion, those flasks that came with cased sets of pistols were intended to be used to load a pistol that hadn't been shot for hours or days.
In this condition there is no danger of loading a pistol directly from the flask.
As far as flasks that use a flame barrier to keep the powder in the flask from igniting, there were dozens of different designs patented in the mid 1800's, all of them using some sort of method of blocking off the main powder reservoir from the measuring tube. Clearly, the problem of ignition of the powder in the flask was known about and many unique methods were designed to prevent it.
I don't have a web link at the moment. I get most of my information about powder flasks from the book named, "THE POWDER FLASK BOOK" by Ray Riling.Thanks for this information. Very interesting. I have never seen such a devise. Might you have a link?