So doing my research on reloading techniques, I find references to fine tuning the sizing process by use of case comparators, including several helpful Utubes showing how. All say the goal when setting up your sizing die is to set shoulder bump back anywhere from .001 for bolt guns (we are talking rifles here) to as much as .004 for semi-autos. Do that and you wring out good accuracy, not to mention extend case life. Or so the story goes. Sounds like good advice, so I decide to put it into practice. So yesterday, I'm setting up my sizing die for some .243.......carefully measure my case.....then follow directions for the dies.......which tends to go along the lines of...."raise ram on your press all the way, then screw in sizing die until it touches......lower ram and give it another 1/4 turn, then lock it down". I have 4 different brands of dies (Lee, RCBS, Hornady and Bonanza) and all pretty much say the same thing. Do that and your sizing die is set. No mention of getting that .001 shoulder bump.......but no worry, I can measure for that. So I do.......and what do I find? My shoulder bump is now EXTENDED by .001. Sizing the case does not decrease shoulder bump....it makes it longer? My first thought is I didn't set die low enough, but quickly realize that once a die is bottomed out, it can't go any lower. So what gives? Here is what I am thinking and if any of this is wrong, feel free to set me straight. First is it seems to me that dies are made to form brass back to SAMMI specs. Both as to diameter and length. How much a die will size any brass thus depends on how much the brass needs to be worked. If fired in a loose, sloppy chamber, it may need a lot. I'm reading where military rifles often have chambers to the large size so most ammo will chamber and fire. Custom and other precision rifles being the other end of the spectrum and may not allow the brass to move much at all. Second is it may take several firings before brass fully fire forms to a chamber. My assumption going in is would do that every time. That may be wrong, or it may be that the guns I'm loading for have tight chambers and are at min SAMMI specs and may not allow much case expansion? I know that for two of them, when I measure once fired brass in a Wilson case gauge, all brass still fits as to headspace and length. So basically, the brass I was sizing yesterday didn't need any shoulder bump. So how did it get longer? Only thing I can think of is the effort required to pull the neck sizer out was enough to also stretch the neck a bit with it. What I didn't do, but now realize I need to do is measure case length before and after sizing. Normally, I'd think of it as sizing forces the metal to go somewhere, but hadn't considered that the friction of pulling the neck sizer out would be enough to stretch the case with it. But as far as setting up the dies for shoulder bump is concerned, one of the ideas that makes the most sense to me when using a bolt gun, is to strip the bolt......and if a fired case will not chamber, keep adjusting the sizing die down until the bolt will just barely close on a sized case. The only way I can see that happening with a normal die is to NOT follow the directions.......in fact, do the opposite. Screw the die down until it touches, then back the die up a half turn. Then start an incremental trial and error process until the the bolt just barely closes. That may be far less sizing than what the die instructions call for. Or forget the technical stuff for now and just follow the directions to begin with? Where is the fun in that?