Tried again today. New position as below:

Firing:

Resulting target, 25m. of the four, upper two are right barrel, lower two left barrel. Leftmost one of each was fired standing, rightmost of each resting as per first photo.

Some unburnt powder:

My 19yo son had a go:

In recoil:

BP and Duplex loads each fired two, only one on paper. Grim. I will work with the NfB loads some more, then the duplex and BP.