In the Army, we used the dime trick. Front sight has wings on either side to protect the front post from abuse. A dime fits perfectly on those wings. Dry fire - the dime should not move at all.
I had various training aides to demo sight picture and breadth control but I always had the troops perform dry firing before qualification. Never failed to qualify a soldier - although, some required several attempts. . Range Officer was one of the most unappreciated "assignments."