BoydAllen
Gold $$ Contributor
Once you have fired the case the first time, which will probably blow your cases' shoulders forward about .021 (Measure before and after and let me know.) you treat die setup just like a rimless case. On a once fired case, I generally set the die to position the shoulder in the exact same place as it was after firing, making sure to remove the primer before measuring the case. After that you can keep an eye on your shoulder to head measurement and when you see the fired case measurement stabilize at its longest value, you can bump back from that. Be sure to check the bump on all of your cases, since the factory anneal will give you variation in bump, and you want to have all your cases function smoothly, or your groups will enlarge, with tight and easier bolt closures in the same target group. When I was helping a friend work up loads for his magnums, with Winchester and Lapua brass, we ran into this, and since he had the budget, he got an annealing machine, which we set to do just enough "stress relieving" to uniform the bump, without taking down neck tension very much.