Missing what I thought was a basic concept on shoulder bump..

[Webster]

So I have thought that I take a fired case from my Ruger Precision 308, full length size and push back the shoulder .002”. Using a comparator with Sinclair 20degree shoulder gauge. I seem to have set up correctly. I will also add that I cleaned the case and annealed it, prior to sizing,

I was under the assumption that with the .002 reduction in shoulder, by bolt should drop free on that case (with ejector removed). It seems that I actually have to back the shoulder back .005 or .006 to accomplish free dropping bolt.

Lapua brass, FYI. Bolt only has extractor.

I tried deburring mouth also.

I would measure the case length with the bump gauge before annealing. It probably doesn’t matter but the heat may expand the case from the original dimension? The normal way of measuring is the gauge hole diameter matches the diameter at mid length of the neck. This location diameter is usually on the blue print. This dimension location assumes the rest of the fired shoulder conforms to the blue print and the shoulder is smaller in diameter than the chamber. Remember your comparing things to a 1 or 2 thou dimension. Would bump needed be determined different if you measured at a different location on the shoulder? The bump gauge doesn’t consider any dimension of the shoulder except the diameter at one location. The bolt doen't have to fall closed with zero effort.

I would just fire, measure for your reference number, anneal, size and bump any reasonable amount for easy bolt closure. No matter how much you bump you will probably never see the difference on the target with a factory rifle. Just shoot and have fun.