O.K... Here goes, I have in the past had rifles with rimmed cartridges that head spaced off the rim. Head spacing off the cartridge rim seems to be quite an accurate way of doing things but now I have a 308 WarBird which headspaces off the cartridge shoulder like so many other rimmless cartridges. I have not been able to find the spec. for headspacing on the 308 WarBird if anybody has a source for this spec. it would be appreciated. As I understand it upon firing a cartridge the shoulder is blown forward, this I am afraid will change the headspace the next time you fire this cartridge unless you full length resize every time you reload? I'm wondering whether I should set my resizing die up so that when I chamber a reloaded cartridge I have the correct headspacing as well? How would I check for correct headspacing? I thought possibly cutting a peice of feeler gauge to lay on the bottom of the cartridge and then checking to see if the bolt will close. Any idea's ??????

That's usually no problem as long as you're using the cartridge cases in the same rifle. When you neck size, the case has indeed swollen to fit the chamber and has little space around it, which many people feel holds the round better centered in the chamber and enhances accuracy. If there's any resistance of the bolt to closing, though, the case has gotten too tight in the chamber and needs to be full length sized. Otherwise you could have a situation (say, on an expensive hunting trip) where the bolt won't close when you need to make a shot.

If you follow the instructions with the die, usually you turn the re-size die till it bottoms the shell holder when the handle is lowered completly. For new brass once fired going into the same chamber, back the die out and with the neck of your fired cartridge blackened by match smoke, slowly back the die down till the entire neck is recized stopping before the junction of the neck. This setup will work fine on bottleneck cartriges fired and reloaded for the same chamber. I would not do this with any other action but a bolt, for semi autos, pumps and levers full length re-sizing is the way to go.

I would add that setting your die to contact the shellholder, while recommended by the manufacturer, is making your cartridge headspace dimension small enough that it would fit any other rifle chambered for the same caliber.

While this is "OK" for a rough and "universal" setting, it is likely that unless your rifle has a "minimum" chamber, your headspace will be enough that the brass is worked excessively. Cases will not last and may separate. Setting my dies to touch the shellholder has been the greatest enemy of case life I know.

As pointed out above, some re-use in your rifle will likely be fine with partial sizing, but you'll eventually want to fully resize to keep them easy to chamber. Once your die has been correctly set, you can back it out with a specer or shim to reduce the amount of sizing to "partial", if desired.

The best way I know to set your die to match your chamber is to take one fired case and increase the neck diameter with a larger expander. In the case of your .308, I'd use an 8mm or .338 expander. Once the neck is expanded, run the case into your sizing die, but with the die backed out 1/8" or more. This will form a new shoulder, well forward of the existing shoulder. Try the partially sized case in your rifle. It should not chamber yet. Begin slowly advancing the die, sizing the case further and trying again until the rifle will just barely accept the case. Lock the die, this is it, the case has just had the shoulder located at the maximum length, to produce mimimum headspace. If cases seem tight after several firings, you might turn the die in very slightly, but not much more, or your headspace will be back at maximum.

By setting the die in this manner, your maximum shoulder length is correct, no matter where your case shoulder is now.

It is only necessary to use one case for this initial setup, but if your cases have already been excessively resized and headspace is large now, you can bump the neck and reset the shoulder as explained above on all of them. There have been a few recent posts regarding false early pressure signs that I would attribute to too much headspace that you may find helpful to see.

BTW, any rimmed (or belted) case, if also a bottleneck, would benefit by this same sizing die adjustment. Headspacing on the rim or belt is not the same as ensuring the shoulder doesn't have to move in and out, thus stretching the body. Any rimmed or belted bottleneck cartridge should use the shoulder to control headspace.

I'm not totaly clear on what the purpose of headspace is to start with, as far as I know the rifle has to have headspace to function properly right? But not to much headspace. I'm thinking set the resizing die until it bottoms out on the shell holder then back off a little until I hit the spec. for this rifle and lock it. Would zero headspace or close to zero headspace not damage the rifle?

Headspace is simply the distance from what stops the shell from going backwards (bolt face) to what stops it from going forward (belt, rim, case mouth, shoulder). There are 2 things that are often called headspace, #1 is what the gunsmith is looking at with the Go (minimum spec) and No-Go (maximum spec) gauges as he cuts the chamber. #2 is what we as reloaders can control with our sizing process.
When fired any "extra" clearance is taken up by driving the shell forward with the firing pin (it has to before the primer can go off). The case mouth and body are than expanded to grip the chamber walls by the pressure of firing. Now the case head is driven back into the bolt face, stretching the brass.
By setting the sizing die to "crush the shell holder" your insuring that the maximum stretching will take place. By setting the sizing die to just "kiss" the shoulder (pushing it back not more than .002), or by necksizing only, you eliminate or at least limit the amount of stretching that's taking place.
Zero or even a slight minus (shoulder .001-.002 longer than chamber, crush fit) won't hurt the rifle, in fact it's not unusual to see in a bench rest rifle, but isn't recogmended in a hunting rifle, due to the potential problems of dirt and fouling stopping the bolt from closing during a followup shot.

Tailgunner is correct and to do this you neck size the case until it will go into the chamber with just a whisp of crush, barely felt and then set the die there...At some point you will have to full length resize, like every 5th loading or whatever your gun decides to take...

I'm a hunter and I full length resize all loads..I have found this to be fine for my use and all my guns shoot about an inch...reloads last as long as they did when I necked sized years ago.... I full length resize because function is my most important need....

O.K. so headspace is just to ensure reliability as far as getting a round chambered quickly and allows the cartridge to even be a bit dirty? So zero headspace is O.K. but to much can lead to a burst cartridge, right?

Right!

And too much headspace will rarely rupture a case, at least on one firing. Machine guns have notoriously sloppy chambers. The problem comes mostly with reloading, sizing the case back down and stretching it repeatedly.