Tender Descenders: 0.2 grams of FFFF Black Powder
Piston: 0.176 grams of FFFF Black Powder
Some black powder spilled out a little bit while manufacturing the Firebolt Jumbo, so I tried to compensate by eye (maybe adding a little extra?)
Note: that the final rod seal is kind of messed up and cut up. It still seemed to seal though by doing a tug test with the inlet port closed up.