Hi,
For the remigton derringer the best round are the n.0 ball that have a diameter of 4,2 mm!!With other(more 4,25 mm) you don' t obtain a great speed velocity..why the zündhütchen don't have much power and the diameter of the barrel is 4,12 mm (electric caliber caliper)
With these you can pierce a tin cane!(in steel)
The best Zündhütchen are the RWS plus that can have a great power!
Ball 4,2 mm+RWS plus=more power than a anics skif A-3000
I have write about in this forum