Bumping the shoulder back.

[cynjon]

In order to know where the shoulder is before and after "bumping", you'll need a headspace comparator gauge such as the one from Hornady. Here's a good video that describes the process and how to use the comparator, as well as full-length sizing vs. neck sizing vs. bump sizing: https://www.youtube.com/watch?v=V2Wt8-VqeAE

[Kingrich09]

In order to know where the shoulder is before and after "bumping", you'll need a headspace comparator gauge such as the one from Hornady. Here's a good video that describes the process and how to use the comparator, as well as full-length sizing vs. neck sizing vs. bump sizing: https://www.youtube.com/watch?v=V2Wt8-VqeAE

Thank you for that link that answered a lot of questions and things are starting to make some sense. Is shoulder bumping something that is commonly done for semi autos or is it strictly for bolt action? Obviously those cases would only be good for the rifle they were previously fired from.

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[cynjon]

Every rifle is different, but I would think that if you are keeping the brass specific to a particular firearm, whether it's semiauto or bolt, then bumping the shoulder would probably provide reasonable reliability and would work fine for 99% of people. If you're talking about life or death "every round needs to chamber 100% of the time" reliability, then I'd be using ammo that leaves more tolerance for fitting in the chamber. When starting with unknown brass, I always full-length size for the first reloading. Load some up with a shoulder bump and see if you have any reliability issues...if not, load 'em and shoot.