Apache: You missed my point entirely. I was trying to tell you that there is NO practical upper limit, and I don't believe using more filler is going to burst a good barrel.
If I were shooting a .54 caliber gun, I would use 30 grains of corn meal by volume, no 40, but I don't think 40 is going to cause you any problems. That is the bottom line.
Would I double that to 80 grains? NO, but ONLY because I am CHEAP, and can see no additional benefit to using more corn meal!! I would not be worried about additional pressure, or even recoil.
If you are hunting Northern Wisconsin, and using Black Powder rather than Pyrodex, you should have no problem with misfires. However, I would be looking at your pre-shooting cleaning and your loading techniques to see if that is not the reason that you were having trouble with the Pyrodex. It could just be the design of the breech, with a Nock-style small powder chamber, and a right angle flash channel that is so small that pyrodex does not get down into the channel when you load the gun. Using FFFg Black Powder will improve matters.
You have to clean the oil out of your gun, and out of the flashchannel on a percussion gun, BEFORE you load the powder. Just firing off a couple of caps WON'T always do the job in all weather conditions. And, if the gun has been stored for any length of time, the oil may have changed to grease, and trying to burn it out is only going to leave a lot of burned, greasy residue in both the flash channel and the bore.
So, always take the time, to pour some alcohol down your barrel, and then shake or slosh the barrel back and forth, one hand blocking the muzzle, and the other blocking the vent hole or nipple. I always remove the nipple on my gun for this kind of cleaning, because the orifice is so small in the nipple. I don't want greasy crud cloggying the orifice behind an otherwise clean barrel. I put my thumb over the hole in either the patent breech, drum, or barrel where the nipple is screwed in, to keep the alcohol in the gun where it can do its job.
I pour the alcohol and gunk out of the barrel by turning the barrel up on end, so it comes out the muzzle. Its always amazes me what color the alcohol changes to, and the occasional floating carbon that come out, too. Easy to see if you pour the alcohol out into a clear jar, like a mayonaise jar. Then cleaning patches, first with alcohol, and then dry are run down the barrel to remove any remaining oils, and crud. A pipe cleaner through the flash channel or vent clear that of any remaining grease, or oil. A small drop of oil on the threads of the nipple, and the corresponding threads in the barrel or breech, and the nipple can be put back in the gun.
If I am contemplating a long drive to get to where I am hunting, I will run a very lightly oiled patch into the barrel just to prevent rust on the now bare bore. When I get to the place to hunt, I run a dry patch down to remove the oil, then load my gun.If I expect to be sitting on a stand, or think it may be some time before a shot is fired, I now run a lubed patch( with wonderlube) down the barrel to grease the barrel in front of the PRB or OS cards, so that the barrel is not rusting while I hunt. If the weather is sub-freezing, I will probably switch to using Ballistol for my patch lube, and for greasing the barrel.
I stopped firing off caps, other than on a range, years ago, to clear my gun, as I generally am hunting deer, and occasionally pheasants, with my shotgun, and I don't even slam the car door where I park my car, to keep from alerting or spooking game.
I also found out at a range one very hot, and humid July, that caps won't burn out oils. I suffered a number of misfires, until I took the nipple out, and gave the shotgun a thorough cleaning, as described above, with alcohol, pipe cleaner, etc-- the whole works. Only then did the gun go off reliably. In fact, it is the ONLY time I have ever suffered a " Hang Fire " in my life, shooting percussion.
