If the barrel is turned into the frame all the way and is still loose, it is unlikely that turning it an additional full rotation is possible.
This means that in order to tighten the barrel and get it snug, you would be turning it past the point where the sight lines up. But if you try to go all the way around, the threads on the barrel or frame will strip.
I would say that the barrel being loose in and of itself is not necessarily a reason to declare that the revolver is unshootable. As long as it is not too loose.
I have had loose barrels on Brass frame Remingtons but never on steel ones.
Before buying a new barrel I would inspect the existing barrel and frame and try to determine why it is loose. If you note damage on the threads of the frame or the barrel, try to decide how extensive it is. It may be that a new barrel won't fix the pistol.
Other guys on the forum have better experience with the formulations that are available to hold threaded fasteners in place. I am thinking "loctite" or some such concoction. I would have two concerns:
1. Will the loctite hold the barrel in place under the stress of shooting it?
2. Might loctite prevent you from ever getting the barrel out of the frame if you decided to do so in the future?
I agree that photos might be helpful here.
My reading of history convinces me that most bad government results from too much government. Thomas Jefferson