Model 12 issue

[Baltimoreed11754]

Bought a couple of M12s in the last couple years. The first was rebuilt into a trench gun and runs like a top. But the second that I rebuilt into a riot gun has an issue. It cycles, feeds, ejects, fires, inertia lock releases, action slide lock releases the slide and it looks great. BUT, if I pull back on the action slide handle to cycle the gun but have not fired it or hit the slide lock button it jams up and takes some wrestling to get the handle forward again. It feel like it’s slipping by something and then jamming. But once I get it unstuck I then can push in the slide lock while pushing forward on the handle and everything works fine. Doesn’t do it every time. I don’t have this issue with the trenchgun. If I pull back on the handle [without firing or pushing in the slide lock] it just stops solid like it hits something in the gun. Nothing sticks or jams. Any suggestions? I might try to swap the trigger assembly's between them just out of curiosity.