I shoot a percussion muzzle loader a lot, and have a shot snake which works in much the same way as that system appears to. The bags are carried spots down(kind of like a sheep's udder). To load, you lift the gate which releases a set powder charge into the measure. The gate then shuts as you pull the measure and pour it down the barrel. Put in wadding, ram home, measure and pour shot the same way, top with an overshot card and ram home. The separate measures are usually considered to be "Irish type". The English type has the measure permanently attached to the snake or flask. There are advantages to both systems. With a snake I like the Irish system which does not require bringing the muzzle of the gun up to the snake, which is up against the shooter's body. This is especially un-nerving if the second barrel of the gun is charged. With a flask, the English Style is not a problem.
There are pretty good pictures of this equipment at the Track of the Wolf website (Shotgunners bags). Much of the equipment is made by "October Country", which also has a web site, and is right up your way.
Best of luck with it!
