Steeltrap, I've only made two caps, and it was frustrating but very rewarding when it was done. Rolf is right, cut down the blank as soon as you know it's too big. In the first photo I had waited too long and bent metal I was just going to file away. The two I made were of thicker sheet, about .090. It bends a bit slower but I was glad for the extra thickness when it came to inletting.
For the tang, I cut some shallow grooves in the block to help form them to the stock curve. Once you get it close, you can drill the hole and screw it into the form, which helped getting it symmetrical.
I mostly used the ball peen hammer, but did use some round punches. They aren't as big as I'd like but did work. I got them from Harbor Freight, they call them doming punches, and a set is about $40. I use them on entry pipes too.
Keep at it! Jack Brooks told me that when forming brass, it's hardly ever ruined, just keep annealing and working it. I recalled that at one point when doing this one, so I fished it out of the trash and sure enough, it eventually fit!!