The Mug I referred to in my earlier post weighs in at 68 pounds. About the 5000 grains. It wasn't per se a proof load in and of itself. Old timers use to fire their pieces into freshly fallen snow. If they saw no powder on the snow they amped up the charge. This process was repeated time and again until they saw unburnt powder sprayed on the snow. They then knew that that was too much powder for their piece and to back off it a bit to be able to utilize all the powder they could in their given piece. Yes 5000 grains was used, but so was a number of other loads all behind a one pound ball. It turns out that the Thunder Mug would completely burn a load of 2500 grains, but just a bit more and you'd end up with unburnt powder. A more reasonable range of loads was suggested from 1500 to a max of 2000 grains. With the 14" tube length I'm sure that the 1500 loading will be more than enough for what I'm trying to accomplish. Sure a heavier payload (5 pounds of lead) would increase pressure more than adding powder would, but the objective was not to see the breaking point of the Thunder Mug, It was to see if it could handle a heavy load with a projectile knowing that in its use there would never be a projectile. I think he did a fine job of figuring out all I needed to know and I'll stick with the 1500 grain loading and wad (NO projectile). Smithy.