Twitch shot not working?

Anyone else having an issue with Twitch shot. Its an upgrade for the pig. But I cant see a button to use it and it doesn’t proc automatically. Using a shotgun if this matters? fully loaded with 3 rounds. Still doesn’t proc.

Thanks,

Edit
I worked it out. In the inventory screen. Each toon can only have one major, one minor an done passive skill active at a time. So for the boar you can’t have run and gun and twitch shot…