Slug Guns
A pity the photo was of actual rifles - none of them was a slug gun aka an air rifle, which shot small metal 'pellets' not bullets.
On another note - yes, shot them in 50s and 60s though, being a girl (!), I had to use my brothers' guns. We lived in an isolated rural area in NSW and had plenty of safe space to practise in. We used a variety of targets, including home-made paper and cardboard bullseyes ones, cans, bottles, trees and yes, birds. I never shot at birds, and would tell my brothers off for doing so, particularly as they did manage to hit some.
They were fun to use, though I was seldom able to hit the targets my brothers set up, as I was short-sighted.