Guns that have a smooth, not a rough, inside.
Smoothbores are old-fashioned and not as accurate as modern guns.
Examples:
The soldiers used smoothbores in the old days.
Smoothbores were not as good as rifles.
The smoothbore was not very accurate.
The smoothbore said, 'I'm not as good as a rifle, but I'm still a gun!'
In the past, people used smoothbores to shoot, but now they use rifles.
The smoothbore was sad because it wasn't as good as the rifle.