Preacher, I've test fired it twice. Both times with blanks and Skirmish Powder (Fg). First time 4 oz., second time 6 oz. Next time I'll try 7 oz.
The 6 oz. load was nearly twice the bang of the 4 oz. I'm guessing over 7 oz. would provide diminishing returns: more $ for not much more bang.
The 4 oz. generated no recoil, the 6 oz. about an inch. I made the charges as described in this forum (powder in plastic baggie, six ply foil). The problem is that makes a pretty thin charge (1 to 1 1/2" thick), so I put about 3 cups of flour on top (within the same foil pack) in order to get a charge length of about 5 inches.
To my surprise, the blast did not eject all of the flour out of the barrel, making cleanup (sponging) a little messier. I might have to change to something else for filler.
Any ideas? I have unlimited downrange exposure, so flying debris is not an issue. Dean