Philip Massaro 
Gun Digest Guide to Advanced Reloading [EPUB ebook] 

From Chapter One:Hello again folks, Mr. Massaro here, welcoming you to the second reloading ammo blog series. We will get a bit more in depth this time, so grab a comfy chair and let’s chat.Shoulder bump, eh? Nah, I’m not talking about some hipster dance, I’m talking about how much we move the cartridge shoulder during the resizing process.Most folks (myself included) will resize a bottleneck rifle case so that it adheres to the specified SAAMI specifications, but that requires working the brass considerably. As we’ve all seen, overworking the brass will make it brittle, and cut the life of our brass much shorter than necessary.