Got some some diabolo pellet molds. Full bore .73 inch 12 guage slugs loaded light to be quiet, and .25 pellets for unlimited ammo with the Hatsan Flashpup.
Got my scale in the mail. Looks like I'm gunna have a good amount of energy even below 750 fps. These slugs weigh a lot more than I was expecting. Borrowed a chrono, but I wasn't able to get it to work. Ordered 2 more on amazon...