I notice in mine PST the zero stop will wander if I turn it hard enough. The key word is hard enough. I have to be consistent if I want to have the same stop each and every time. Also I notice that at different temperature I will have a different zero stop as well. This may be due to and metal expanding and contracting. With the turret have very fine adjustment and little expansion or contraction on the brass shim will definitely have an effect on the zero stop.
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