You are right that the first mark indicates 2 grams of the semi-smokless Schultz powder.

However, the second mark, "27g Bl" is for the shot charge. It is not a reference to an
alternate black powder load (in grams, not grains). You might note that 27 grains of black powder
would only be about 1 dram, far too little for a charge. On the other hand, 27 grams
(the unit used) of black powder would be about 15.5 drams of black powder, a serious overload.
The mark indicates a charge of 27 grams of lead shot, an entirely appropriate shot load for a 16 bore.

I would like to ask you to duplicate your posts on the 'Classic' Firearms Photos & Archive forum
if it wouldn't be too much trouble. This is a perfect display to appear in that
permanent archive forum.

Thanks,
Curl