A proof test is to establish a point at which you should stay below by 10% be safe. When they talk about minimum proof they are refering to legal requirements each individual gun should be tested to. If you check all the known info you will likely come to the conclusion that 75 gr of black or pyrodex will give you the pressure that those guns were tested for; I wonder how old that law is because thats about what they used for a load in the civil war days does any one happened to know? Actually I believe proof testing was developed to fined flaws in a gun barrel [like laminations for instance] there was some testing of custom made muzzleloadingguns done by some gunsmiths back when custom Kentucky long rifles and Hawkens were popular where they used twice the ball weight and two patched balls and used a gun vise in a protected area and set them off from a distance, I know when I had Marcus proof my Hawken he used 240 gr FF black and two patched balls then magna fluxed it [ that is an interesting process]. I guess I am a bit leary of the spanish barrels, the processes they are made by are prone to flaws and shooting twice the load that it is proofed too just does not seem real smart as it is supposed to work the other way around, and even though they are not in the same strength range as the knight or TC barrels they do make some fine barrels if you do not happen to get on with a flaw in the metal. Lee