I don't really understand where it came from. The stock G39 I have has absolutely no barrel wobble, yet my main one, which I've only opened up twice - once to replace the hop nub and once to try to reinforce the barrel - has a silly amount of play in the barrel. It's also completely independent of the barrel nub and as far as I can tell stems from the hop unit directly, which is a silly way to hold a barrel in place. I mean the barrel is basically being held by two tiny little phillips screws in a pot-metal hop unit and free-floats from then on. I tried using tape to make a tighter seal in the hop unit but it seems to have had no effect. I'm not missing a shim piece or something, am I?