I could have sworn that my first handi I had "shot loose", but it could have been a dud from the start. At its worst it actually rattled (it had a .006" gap, but as Fred said even that one as loose as it was was easy to fix (I just made a shim with a piece of feeler guage). My second has not shown any loosening yet though it is just a 204 ruger. And my third (a 22 hornet) seems to be starting out the tighest (~.001" before I put it on layaway).
My guess on "shooting loose" is that there is a bur or high spot in the hindge system that flatens out somehow, either wear or the stress of firing. it's only .0015" between OK and not OK so it does not take much to hide an issue or make one. Though I think if it is to show up I would think it show up sooner than later.