[Pollster1]

Also, what other guages than the 12ga would be good to concentrate on?

My personal opinion is that there are no other gauges besides 12 ga. You can get reduced recoil in 12 ga. You can get tactical loads. You can get birdshot, skeet loads, turkey loads. Why buy another weapon?

[Utilizer]

Why buy another weapon?

Ammo availability for when TSHTF. What is most commonly used is likely to be most commonly available later. If there is another round as popular as the 12ga then it makes sense to have a weapon capable of using it when necessary.