Does it wobble with Hulls in the gun??
I makes no difference if loaded or empty.
I found the following video on YouTube. It's not me nor my gun in the video, but mine was almost exactly like this; no perceived motion when pulling up or down on the barrel/foreend, but when you moved it side to side you'd notice (more feel than see) a slightly wobble and hear a faint clicking sound. I tried a piece of regular masking tape in the same place this guy put copper shim tape, and mine also immediately felt solid and I can't hear any more clicks. It still opens and closes with the same effort as before.
I know this tape will quickly wear out, but tomorrow I'll go out a shoot a few rounds and if it seems right I'll try to find some copper shimming tape.
(I plan to shoot just light BP loads in this gun.)