I would go with the 50. Also, shoot 777 instead of black powder. I use the pellets, 2 per round. This stuff is a LOT easier to clean up compared to black powder residue. Just run hot water through the barrel, swab it out, apply a rust preventative oil with another patch or brush and you are done. I also use Gorilla Grease, the purple stuff, as thread lube on the breech plug.
2019 VW Passat 2.0 liter gasoline DI engine, DI, 1,100 miles, Castrol Professional VW 508 0W-20
2017 VW Golf All Track 1.8 liter gas engine DI, 24,500 miles Castrol Professional VW 505 5W-40