Looks like the pipe plug in the section of pipe telescoping over the barrel probably moves forward. Wouldn’t be a problem to file, machine or drill and screw a firing pin onto it’s face and the hammer would drive it home. The plug and pipe act like a shroud around the breech.
One thought anyway...
And there are those who think by drying up the supply of guns, they would disarm us. Remember the “Liberator” pistols of WWll? They were a bit more sophisticated than a zip gun but not much. A single-shot .45ACP. the idea was to sidle up to a german sentry, stick the “Liberator” in his ribs, pull the trigger and take what he had.