Hi NDPronghorn,
I'm very familiar with the problem you're having with mounting your scope. I thought I would never get my TAC 15 shooting!
If you have a newer HHA Optimizer you shouldn't need to shim the scope IF all the components you're using are manufactured pretty close to specs. I had an older HHA Optimizer which Harry and Brad Ham at HHA Sports changed out for me. They are great guys!
That said, you may have a combination (your TAC 15 upper, HHA Optimizer, scope mounts, scope rings, etc.) that is at the extreme end of the specs and the combination just won't align like you want. The answer I found, through trial and error, was to use a set of Burris Signature Zee Rings and ***-Align Offset Inserts.
You might use the PVC shim solution as jon.henry755 suggested (and as Super 91 used), but in my opinion there is a potential problem using a PVC shim in one of the rings and that is the possibility of bending your scope. As you are aware the steel rings grip in a straight line and if they are tilted (ie. on different planes) they will only grip with the edge of the ring. The Burris rings and inserts will grip the entire surface of each ring. There is an excellent article here on LRH in the ARTICLES section discussing these rings and inserts and the reasons for using them. I don't remember the authors name.
The Burris Signature Zee Rings come in 30 MM or 1 inch to fit whatever scope you're using; you'll need the Weaver Style for the Optimizer rail. An accessory kit (Signature ***-Align Offset Kit) is also available and includes one .005", one .010" and one .020" offset inserts. I ordered accessory two kits when I ordered my rings.
Len may have them here in the LRH Store. If not, you can do a google search for them. You will find several sources, but not everybody will have them in stock and prices will vary.
Read the article I referenced, read Jon's article on the HHA Optimizer, let us know what you decide and we'll go from there. Ask any questions!
Regards,
Buzzard Bait (Russ)