This indeed is very demanding and brilliant scientific research work proven by many firing tests carried out by one of the cleverest members of our forum who has gone deepest into search - which of yourse is you, my friend!
You finally have managed to explain the phenomenon why so many handgonners shown in period artwork are depicted right at the moment of aiming (and sometimes firing) their gonnes without a lock mechannism, and nonetheless holding them firmly with both hands. At the same time the honor of discovering the actual practical reason of the often unusually wide Gothic touch holes is due to you: ignition delay
when using the fine meal powder
In the first image below, a detail from a Nuremberg painting of Die Schlacht im Walde
(The Battle in the Woods), 1502, shows such a handgonner - and please note the white smoke curling up from the touch hole immediately before the shot rings out
although no piece of tinder can be seen anymore!
We should not forget, however, that touch holes wide enough to be filled with that much priming meal to delay the shot long enough to grasp the smoldering gun and aim it with both hands only seem to have appeared during the 15th c. Late 14th and early 15th c. handgonnes were still equipped with quite small touch holes and therefore seemingly required two men: one to aim and the other the ignite the gun (see last picture below of 1437) - Richt- und Feuerschütze.