I have one of those, Rod. Tap-O-Cap by Forester. Quite a tool. At that time, late 70's here, all of our beer cans and pop cans were thin steel. It still worked, but was hard on them tool's teeth. I had to sharpen it a few times. Still works though. Aluminum would be a snap. The steel caps, would barely spread a bit upon firing. I would rinse them in water, then spread out to dry. Once dry, I simply put another drop of compound in them. Once dry they were good as new.
Instead of using kids caps, I made my own detonating compound from 5:1:1
Potassium Chlorate, Sulfur, charcoal.

I used appocthocary's potassium chlorate, sublimed sulfur and lacking real charcoal, I used ground up briquets.

The mix I made may have been extra volatile due to the flour of sulfur (sublimed)& chemicals in the Briquets as well as due to mixing it up in a slurry(with water). I dried it then carefully, wit my fingers, broke it up into powder.
I would put a drop of slurry into each home made percussion cup, then let it dry.

As to it's power I also tried making explosive bullets with it, for my custom .58 S. Hawken rifle, as well as filling the little cavities in .22 Stinger ammo, then smeared the holes over with beeswax. The 'loaded' stingers didn't hold much of the powder, but would cut off a 1" willow stalk with one shot.
I filled a 3/8"x1/2" hole in a shallow skirted (modified plunger) Minnie Ball, then smeared beeswax over that. 3 of those would cut off a 13" aspen tree, leaving the blasted area blacked.
That was fun, but likely dangerous. This was about