No slide/pump/trombone allowed. A technical limitation independent of time period.
A smoothbore single shot or double could be used in forager, the best example being the M1881 trapdoor "forager" 20 ga. BUT! As we use CAS spec ammo, we have a Minimum bore of 20 required, max of 10. This would preclude the use of the various modern .410 smoothbore lever rifles. I suppose you could use one of these as a rifle in the "Militia" class, but would be limited to single projectile ammo.