This is not a recommendation, just something I did once. My dad had an old H&R single shot 12ga shotgun that the barrel was loose as you describe. I took some thin brass shimstock and placed it in the barrel hinge until the barrel was tight but still opened and closed freely. That was 40 yrs ago and it still works fine, although it hasn't seen a tremendous amount of use, but it has taken a turkey by my dad at age 70, his first, a few years ago! I have shot it with 2.75" magnum turkey loads and it shoots fine, but since it is so light, dad wouldn't shoot anything but standard high base hunting loads and he says that's more than he really likes, but took the turkey with it just fine... :grin: