the average person produces about 5 cups of urine in a day, and a gallon is 16 cups, so a group of people could easily produce anywhere between 1 and 3 gallons every day. the standard drum size is 55 gallons, so that’s easily obtainable. it’s a very slow synthesis, lasting 6+ months, you’d have between 3 and 10+ drums full of urine saved up at that point.
the average black powder musket or rifle gets about 50 shots per pound of black powder, and it takes a good minute or so to reload if you’re skilled, so you really dont carry that much powder around with you at any point in time. I figure you wouldnt need more that 5 pounds of it every month in a survival/hunting/defense against random invaders (rural setting) situation.