>>382730810
Position the two meshes how you want them. First select finger mesh, then ctrl click your ring mesh. Then switch to weight painting mode, and under the "weights" tab in the top left of the edit screen, there will be a button called "Transfer Weights". This is what you want. 

There are a few different options for how to determine which weights will be used, I tend to use "Nearest face interpolated" the most often. If you want to transfer weights for all the bones on the armature, you can set the source to "By name" and destination to "Active". If you just want to do weights for one vertex group, which you might to avoid interference from other fingers, you can set source to "Active".

Hope that's not too confusing