Re: Hand loading for Long range 1: brass case prep
To become a fisherman you have to think like a fish.
This is my attempt to think like a shell casing.
When a shell is fired, the brass expands to fill the chamber, the web section of the brass is unsupported by the chamber to a large degree so the strength of the case does all the work there. After the pressure is released the case springs back slightly, say a thou or 2, which allows the casing or brass to be extracted. You can neck size, reload and fire the shell again and again and if pressures are not excessive this can be repeated quite often. If you full length resize after each firing the die will size or squeeze the brass to the shape of the die and when the brass is removed from the die it will spring back by a thou or 2. The shoulder may not be set back at all, it may in fact be pushed forward depending on the die dimensions and the fired brass dimensions.
If you want to know exactly what is happening you have to measure:
http://larrywillis.com/
http://www.hornady.com/store/Bullet-Comparator-Kits/
If, for instance you have a rifle with a snug or min headspace and a shell chambers with some resistance it will come out shorter (headspace dimension) after firing. If, a low pressure load is fired it will also come out shorter. If, you have a rifle with generous headspace (still safe, after all nobody would want to knowingly fire a rifle that had excessive or service headspace) the brass will be longer than it went in.
For the most part, if you buy a new gun or 2 and buy good quality reloading equipment and supplies you will in all likelihood never have any problems and really won't understand what all the fuss is about. But if you buy a fair number of gunshow rifles or used ones you will get an education. I've had the fun of experiencing first hand excessive headspace, oval chambers, dimensionally small dies, short dies, crooked barrels, barrels installed crooked, stepped and improperly machined bolt faces, oversized firing pin holes, sharp primer piercing firing pins and some stuff I have forgotten.
The 101 and 201 posts in this section are a good read, they explain all this better than I can.