I have a family member that was a police officer in a rural location. They have often had cases of farmers who kill themselves with shotguns, and it surprisingly often occurs that they have to shoot themselves more than once in the head.
In this particular case you're comparing apples to oranges.
Shotguns are very different from a standard .38
First is the obvious difference in projectiles, which can make a huge difference.
Second the .38 (in all likelihood) was a pistol, whereas a shotgun is the length of a rifle. A pistol you can hold it to the side of your head and pull the trigger.. you can't really do this well with a shotgun, which means you're more than likely going to put the gun under your chin and try to get to your brain the long way.
It's somewhat logical that someone might need to shoot themselves twice with a shotgun, not so much with a .38.