Zero unless you count the DC Navy Yard or Colorado Theater shootings as an acts of terrorism. Both involved shotguns.
Yes, you're right.
From Wikipedia:
In its broadest sense, terrorism is any act designed to cause terror.[1]
In a narrower sense, terrorism can be understood to feature a political objective. The word terrorism is politically loaded and emotionally charged.[2]
A broad array of political organizations have practised terrorism to further their objectives. It has been practised by both right-wing and left-wing political parties, nationalist groups, religious groups, revolutionaries, and ruling governments.[3] The symbolism of terrorism can exploit human fear to help achieve these goals.[4]
I think it's always a plus to define the words we are discussing. "Terrorism" obviously has different nuances.