This is mostly repost from something I put in Modeling, which I’m sure now should have gone here. Sorry if that’s irritating.
I’ve actually moved beyond the problem, so this isn’t so much a cry for help as a bit of curiosity. I had a finished rig, and was weight painting it. I discovered that x-axis mirroring was only working on those bones that sat on the centerline of the body, like the spine bones. Bones labeled bonename_L and bonename_R were not mirroring, so I had to put a good bit of annoyed effort into duplicating earlier work on the other side. Some things I’ve read since then suggest to me that labeling them bonename.L and bonename.R would have worked better, but I’m not sure that’s true either.
My question is this: having already weight painted the mesh around bonename_L, if it has not automatically mirrored, is there a way to make bonename_R pick up what I’ve already done on the left side, short of actually painting it?
Also, if anyone can venture an explanation as to why mirroring didn’t work, that would be nice to know for next time. The obvious answer of “you didn’t have x-mirroring turned on” is incorrect. I checked, promise.