Check this thread out. The poster seems to have had a similar problem to you, and managed to solve it. Mine works fine, and I don't quite follow what he did to resolve it.
Extraction problems with my BTVS - RimfireCentral.com Forums
You may want to post at this same forum your request for a synthetic stock. Many replace them with fancy ones at $200+ a pop, so there should be synthetic ones for sale. Sharp Shooter Supply has stocks, but I don't think synthetic ones.
Ron