I found a reference to Tasco TR scopes in an old post here: TR scope info?. It appears that the rings are not caliber specific but rather listed by approximate ballistic data. Once you know your specific rifle/bullet performance you select the proper ring.
Here is the data that was posted there, I put it in a table so it was easier to read.
This is for a Tasco TR 6-24x40 scope (it may be the same for all their scopes) and would be a place to start if you can't get anything better.
(I assume it is based on a 100 yd zero.)
I'd guess C or E for a .223 AR