shotgun squads should be a small very quick squad who fights better and better the more pressure they get.
they shall eat the soldiers, but also could throw grenades Throw Sticky Bombs, have a reload specialty and have a the radio operator.
the radio operator can call for help from all other shotgun squads. This means that all other shotgun squads will make attack-move to the squad who called for help.
when using the "reload" specialty, all shotguns will reload and therefore they are better prepared to kill the next squad they see. it takes time to reload a shotgun when you have to put every round in individually.
when they throw the grenades they throw something like 4 this specialty is called "Clear building." since it can only be used on buildings, it will kill everything or almost everything in the building.
"Throw Sticky Bombs" is just an ordinary Sticky Bomb.
this one squad will be weak against vehicles because they can only throw Throw Sticky Bombs but they'll be good to fight in urban environments. they are thrown out by plane but must return to the base to get new soldiers. they are bad at long distance but they are fast and can therefore run near the enemy and fight where they are best. Since a shotgun certainly is not good to kill people in buildings they can therefore, throw a handful of grenades in to the building.
now they can a bit of everything, but this are mainly designed to kill people at close range. a cool device to have to circles around individually and annoy the enemy where it hurts, and if the pressure becoming too big for even the guys this, they can call for backup for example if they encounter a Stug IV.
Quite honestly who in their right mind would replace a Calliope for a Jumbo?