IME, I've reloaded for a lot of my closest hunting friends for the past 40 years-in addition to rolling my own in 15 years of BR competition. In doing so, I have universally found the desired accuracy lies much closer to the upper end of load spectrum at the fringe of safe chamber pressure than anywhere near the bottom. My # 1 goal after safety is producing accurate loads and I learned to achieve this end that one must realize that brass is an expendable commodity. Not very many shooters (other than youths) will be satisfied using a gun with a cartridge capable of .308 ballistics downloaded to those of the 30/30.Using a full length die to "neck size" means that you are partially sizing the whole case unless the case has a high degree of taper there will be some contact with the body of the case.
I do a lot of work with metal and have for years. Cartridge brass is just 70% copper and 30% zinc. It age hardens and work hardens - like all brass. if you apply heat it softens. The more heat and the longer you hold it there the softer it will get until it reaches its base state or the zinc boils off.
When you fire a cartridge it expands to the size of your chamber. What happens next depends on how soft the brass was before you fire it. Soft brass is malleable, it changes shape and holds that shape very well. The harder it gets the more it "springs" back toward the shape it started with as long as it is not stretched to the point where it fails (cracking). The only way a brass case can get any longer or wider than the chamber is if the pressure is high enough to expand the CHAMBER more than the brass can rebound from. You can theoretically never size your brass if the neck of the chamber is small enough to allow the brass to spring back to the size it was before. Real life isn't like that. Chambers are machined in mass produced rifles so they will chamber any version of new cartridges made throughout the world. Your fired case is going to expand to fit the chamber and the neck will also expand. You need to squeeze the neck back to a point where it will hold a bullet more or less firmly. This growth of the brass causes it to get longer in the only place it can freely move, into the neck. That is why we have to trim the case after a few firings. I have neck sized cases for the last 35+ years and have never had to run them through a full length sizing die after they have been fired in my gun. I hunt with the same ammunition that I shoot targets with and have never had a failure to feed or a tight bolt close. If you run into those problems then your load is making too much pressure in your gun under your conditions (even if it is not at the maximum listed load). The pressure has to be high enough to expand the chamber in order for the brass to expand to the point where it sticks in the chamber. Your brass should always exit and enter the chamber without undue force.
As a new loader 48 years ago I started loading using the Lee Loader in a box. It only sized the necks of bottle-necked cases. When the cases started getting too long I got a trimmer and cut them back to the "trimmed" length listed in the book. (not a bad practice) When I switched to using a loading press and all the stuff that goes with that, I set the dies up in the press the way the instructions told me to (always follow directions). I began having split cases and case head separations because I was taking fired cases that expanded to my rifles chamber and then squeezing them back down so they would have to expand all over again. (my gun has a very large chamber) So each time I fired a case and squeezed it back into shape it was getting harder and harder until when it tried to expand to the size of the chamber the body of the brass would split. In other situations the expanding case was locked by the pressure in the forward part of the chamber and the pressure pushed the back of the case to fill the chamber until it was so thin that it would split around the brass just above the solid web which is called a case head separation.
I told you all this for just one reason: Set your dies up to match your chamber not by the instructions in the instructions that comes with them. Take a case that was fired in your gun and lube it lightly, brush the inside of the neck with a brush that is run on the lube pad, back your die so it misses contacting the raised ram by at least a half of an inch. Set the lubed case in the ram (shell holder) and raise the ram. With the decapping pin backed out (up into the die) screw the die down as far as you can with the ram held at the top of its stroke. Drop the ram and inspect the case. If it has not been sized at all (no squeeze marks on the neck or it has just a bit on it we can continue. Measure from the top of the neck (or bottom of the sized part of it) to the top of the shoulder.
Take a marker and color the neck and shoulder and just below the shoulder on the body of the case. Move you die down almost as much as the measurement you made from the top of the neck to the shoulder. It is best to leave wiggle room so if your not sure error on less movement of the die. Put the case back in the shell holder and raise the ram all the way up. Hold it there for a couple of seconds and then lower it. Look at the case neck to see how much has been sized. You want to keep screwing the die down until it just gets to the bottom of the neck. Take small steps 1/4 turn of the die is a lot of movement so go slow (you will only have to do this once with each die). Once you get all of the neck sized you are going to watch the shoulder of the case for contact marks. As soon as the die comes in contact with the shoulder, STOP. You lock the die in that position with the jam nut and set screw. Now lower the ram about 1/4" and hold it there while you screw the decapping rod down until it makes contact with the case. Move the ram back up to see if the primer falls out (it should). If it doesn't the screw the decapping pin down a bit more testing it at each adjustment. When the primer falls out then you use the lock nut to lock the decapping rod in position. Your full length sizing die is now set for your chamber. You can follow the instructions for the seating die but don't use the crimping part of the die. You won't need to crimp for your bolt action rifles.
Also, following Matts post, I invested in quality measuring tools and gauges early on as I found actually measuring changes in case dimensions is magnitudes more reliable than trying to discern "rub marks" left on cases and interpreting what they are telling me.
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