Daryl,

I read the text on the Bavarian wall gun once more, now I found mention of the original bullet:
"Die Rundkugeln wurden gepflastert geladen" - round balls were loaded with a patch.
Sights in this original form up to 600 paces. Powder charge not mentioned.
I think they were not using that much powder back then, compared to the loads you are using now.

1860 a new Minie-type bullet was introduced, diameter 22 mm, weight 101.7 g (1569 grains),charge 7.656 g (118 grains, seems not much). New rear sight installed, graduated to 1400 paces which will be about 1050 m.

In 1877 the guns were obsolete and sold.