Steve - I am surprised you recommended such a thin patch with a small ball - perhaps a typo on sizes. A .012" patch will only bring the .025"-under ball to .0005" under bore size, per size, .001" total smaller than the bore - with no compression at all to the lands - what abotu the grooves? - the gas cutting from flame and gasses blowing down all the grooves about this combination will incinerate the patch. The patched ball combination must reach the bottom of the grooves or very nearly so. All the barrels I've ever shot ahve required ball-patch combinations to be .004" or more OVER groove diameter creating compression in the bottom of the grooves. This prevents any gas blowby and ensures clean shooting without fouling buildup.

So- if the ball is .022" under bore size and the bore size(not grooves) is 1.015", the ball would be .990" in diameter. If the grooves are .012" deep, the groove depth is 1.015 + .024" = 1.039". A .99" ball would require 1.039 - .99 = .049". .049" divided by 2 = the patch required to reach the bottom of the grooves which would be .0245". 12 pound denim should work OK. This will run around .023" to .025" in thickness.
The muzzle should be crowned like Steve's build of the single 2 bore rifle of Bigdog's gun. I would further smooth the angle of the grooves and tops of the lands with emery cloth on a tool or my fingers, rotation the barrel. It's a nice crown for loading snug combinations - snug combinations shoot cleanly, no buildup of fouling and no wiping while shooting needed.

Mink-oil as sold by Track, or SPG bullet lube mized with neetsfoot oil. Both of these work well. The SPG mix probably better of the two. SPG is a bullet lube for BP ctg. bullets. Mixerd with neetsfoot oil, it makes a good patch lube grease. Try 50/50.

Good shooting.