Black powder is a weak powder ? .......hmmm - under normal circumstances - yeah...............
This ole cowboy blew the nipple out of a 3/4 inch wall post hole gun with a half charge of powder - just shredded the metal and tore the nipple right out - lord knows how far up it went but it landed on the tin roof of my machinery shed about twenty seconds after it went off - plink!- tinkle tinkle - plop - rolled right off the roof and dropped on the dirt not twenty feet from the liftoff position - couldnt repeat the whole thing in a million years - ok where wuz I ? Yeah weak blackpowder ? If you give it somewhere to get out - yeah its weak - but lock it up tight enough - barrel obstruction - whatever - it will still get out - so my prediction here is - pour a hundred grains of black down a caplock barrel - plug the barrel solid (I mean solid - no escape route at all) touch it off (from behind the nearest tree) and you will blow the nipple clear out of that gun - probably the nipple drum too - and if all that is really well built you probably split the barrel - blackpowder under the right (or wrong) circumstances is well capable of generating over 100,000psi. Never assume that you cant come to grief with blackpowder!