A while back a friend was having trouble with inconsistent shoulder bump. I thought that this would be a good topic write a bit about since it happens rarely, but can be maddening. So what was happening was that they were full length sizing their brass, and after spot checking several pieces of brass, they found that the shoulder bump was inconsistent. Target was .002″ and the results would vary up to .008″. This was brass that they had already been through several reloads on. We need to remember that this is a simple problem. The shoulder is being pushed back further in some cases and less in others. That said, there are a number of variables that can affect that. So what information do we need to troubleshoot this logically and where did it go wrong? Well, here are the steps that were recommended for troubleshooting, and why.
Measuring
One of the first things that we can look at is how the measurement is being taken. With something like the Lock-N-Load® Headspace Comparator, you can measure the the distance from the base to the center of the shoulder. So the first thing to do is to make sure the calipers are calibrated and that they are holding their calibration. Next, we make sure that the comparator is set up correctly. Hornady’s instructions say to “select and insert the proper Bushing into the Body, then position the assembly on your caliper blade. Close the caliper blades snugly to align the assembly with your caliper, then tighten the Set Screw and Thumb Screw.” That last part is key. Don’t tighten the set screw first. In addition to checking the tools, measure the cases before sizing to see if there is wide discrepancies in the length before the sizing is done.
Clean Dies
The next step is to make sure your sizing die is clean. Use some brake cleaner, scrub with soft brush if necessary, and then lubricate/oil with something like gun oil, OneShot, etc. and then pull a tight fitting cloth or a shotgun mop through the inside to remove excess. Visually inspect the inside of the die, and your brass for any signs that there is debris or imperfections that could be catching the brass inconsistently. It’s not a bad idea to apply an anti-corrosive to the outside of the die as a last step.
Press Linkage
This is less likely, but it is quick to check the linkage on the press to make sure that everything is tight and there is not anything causing excessive play in the linkage of the press.
Case Lube
Make sure that the shoulders aren’t getting lube on them, and make sure that the cases are getting lubed consistently. If using an expander ball during this step, then it is also a good idea to make sure the insides of the necks get brushed clean, and then use a little dry lube on the inside of the neck. This will make sure that the expander ball isn’t binding inside the neck.
Annealing
Annealing will certainly help with consistency, provided it is properly done. Without annealing, the brass could be springing back after sizing if it has been work hardened. In this case, that would be excessive spring back however. But, if everything else has been checked, it is another variable that can be explored.
Conclusion
Hopefully this helps someone who runs into this frustrating issue with inconsistent shoulder bump. If you run into something different, or have something that would improve this process, please leave a comment.